Night sweat feels different from simply being warm.
You wake up damp. Your shirt sticks to your skin. The pillow feels humid. The blanket suddenly feels too heavy. Sometimes the room is not even hot, but your body acts as if it has been sleeping under a heater.
That moment can feel confusing because sleep is supposed to cool the body down, not turn it into a furnace.
So why do you sweat at night?
The answer sits inside one of the body’s most important control systems: thermoregulation. Your brain, skin, sweat glands, hormones, blood vessels, metabolism, immune system, and sleep cycles all help manage body temperature. When one of those systems changes during the night, sweating can appear.
Sometimes the cause is simple: too much bedding, a warm room, alcohol, spicy food, or stress.
Other times, sweating at night can reflect hormones, low blood sugar, infection, medication effects, thyroid activity, sleep apnea, or another health condition.
The key is not to panic.
The key is to understand the pattern.
You may sweat at night because your body is trying to release heat, respond to hormonal changes, manage stress, fight infection, regulate blood sugar, or react to medication, alcohol, or a warm sleep environment. Sweating is one of the body’s main cooling tools. When the brain senses that body temperature is rising, it activates sweat glands so evaporation can help cool the skin.
Night sweating can be harmless when it happens after overheating, heavy blankets, a warm bedroom, late alcohol, spicy food, exercise close to bedtime, or emotional stress. It can also happen during menopause or perimenopause because hormonal changes can trigger hot flashes and night sweats.
However, repeated or drenching night sweats deserve attention, especially when they occur in a cool room or come with fever, unexplained weight loss, persistent cough, pain, fatigue, swollen lymph nodes, chest symptoms, low blood sugar symptoms, or major sleep disruption. In those cases, sweating at night is not just a sleep inconvenience. It may be a signal worth discussing with a healthcare professional.
What This Means Inside the Body
Sweating is a temperature-control mechanism.
Your body tries to keep its internal temperature within a narrow range. The brain, especially an area called the hypothalamus, helps monitor and regulate that temperature. When the body needs to release heat, blood vessels in the skin can widen and sweat glands can produce sweat.
Sweat itself does not cool you just by appearing.
It cools you when it evaporates.
At night, body temperature normally changes as part of the sleep cycle. The body usually begins to cool before sleep. Skin blood flow increases. Core temperature gradually drops. This cooling pattern helps support sleep.
But if the body receives a signal that heat is rising, if hormones shift, if stress chemicals activate the nervous system, if blood sugar drops, if infection produces fever, or if the bedroom traps heat, the sweat system may turn on.
This can happen suddenly.
You may wake hot, damp, chilled afterward, or both.
That chilled feeling after sweating can happen because wet skin and damp clothes lose heat quickly. The body first overheats or activates sweating, then cools too much on the surface.
Night sweats are not one single condition.
They are a symptom with multiple possible mechanisms.
Main Biological Mechanisms
Thermoregulation: The Body’s Cooling System
Thermoregulation is the process the body uses to control temperature.
When the body becomes too warm, the brain can trigger sweating and increase blood flow to the skin. Sweat glands release fluid onto the skin. As that fluid evaporates, heat leaves the body.
At night, this system can be activated by external heat or internal signals.
External triggers include:
A warm bedroom.
Heavy blankets.
Non-breathable pajamas.
Memory foam or heat-trapping bedding.
Poor ventilation.
Sleeping with too many layers.
Internal triggers include:
Fever.
Hormonal changes.
Stress.
Low blood sugar.
Alcohol.
Medication effects.
Thyroid overactivity.
Sleep disorders.
This is why the first question is simple:
Is the body sweating because the environment is too warm, or because an internal signal is activating the sweat system?
Both can feel similar.
The pattern helps separate them.
Sleep Temperature Naturally Changes at Night
Body temperature is not flat across the night.
It follows a daily rhythm. Core body temperature usually falls as sleep approaches and remains lower during much of the night. This cooling is part of normal sleep biology.
If the room, bedding, pajamas, or mattress traps heat, this normal cooling process can be disrupted. The body may sweat to get rid of excess heat.
This kind of sweating often improves when the sleep environment changes.
A cooler room.
Lighter bedding.
Breathable sleepwear.
Better airflow.
Less heat-trapping mattress material.
This type of night sweating is usually mechanical.
The body is simply trying to cool itself.
Hormonal Changes and Hot Flashes
Hormones can strongly affect sweating.
During perimenopause and menopause, changes in estrogen and other hormonal signals can affect the brain’s temperature regulation system. This can trigger hot flashes during the day and night sweats during sleep.
A hot flash is a sudden wave of heat, often felt in the face, neck, and chest. When it happens at night, it can cause sweating and wake the person from sleep.
Night sweats related to hormonal changes can feel sudden and intense.
The person may wake flushed, wet, and uncomfortable even if the bedroom is cool.
Hormonal night sweats can also occur in other situations, including pregnancy, postpartum changes, some hormone therapies, and certain medications that affect sex hormones.
This does not mean every night sweat is hormonal.
But hormonal shifts are one of the most common body mechanisms behind sweating at night.
Stress, Anxiety, and the Sympathetic Nervous System
Stress can make the body sweat even when the room is not hot.
The sympathetic nervous system is the part of the nervous system involved in alertness, threat response, and physical activation. When it becomes active, heart rate can rise, breathing can change, muscles can tense, and sweating can increase.
At night, stress does not always disappear just because the lights are off.
A person can fall asleep with the nervous system still on high alert. Worries, emotional pressure, nightmares, trauma responses, and anxiety can all increase nighttime arousal.
This can lead to sweating, sudden awakenings, racing heart, or feeling hot and tense.
In this case, sweating is not mainly about temperature.
It is about activation.
The body is acting as if it needs to respond to something.
Infection, Fever, and Immune Activity
When the immune system reacts to infection, body temperature can rise.
Fever is part of the body’s immune response. When fever breaks or body temperature shifts, sweating can occur. This is why sweating at night can happen with viral infections, bacterial infections, and other inflammatory states.
Night sweats linked with infection may come with:
Fever.
Chills.
Fatigue.
Cough.
Sore throat.
Body aches.
Weight loss.
Reduced appetite.
Swollen lymph nodes.
Persistent symptoms.
This does not mean every night sweat means infection.
But if sweating is drenching, repeated, or paired with fever or unexplained weight loss, it becomes more medically important.
The body may be sweating because the immune system is active.
Blood Sugar Drops During Sleep
Low blood sugar can trigger sweating.
When blood glucose falls too low, the body releases stress hormones to protect the brain and restore glucose availability. This can cause sweating, shakiness, hunger, anxiety, fast heartbeat, nightmares, or waking suddenly.
This is especially relevant for people with diabetes who use insulin or certain glucose-lowering medications, but low blood sugar symptoms can also occur in other contexts.
Nighttime low blood sugar may cause:
Sweating.
Shaking.
Hunger.
Fast heartbeat.
Anxiety.
Confusion.
Nightmares.
Morning headache.
Waking suddenly.
Feeling weak.
If night sweating comes with these symptoms, blood sugar deserves attention.
The sweat is not random.
It may be part of the body’s emergency response to low glucose.
Thyroid Activity and Metabolism
The thyroid gland helps regulate metabolism.
When thyroid hormone levels are too high, the body’s metabolic rate can increase. This can make a person feel hot, sweat more, lose weight unexpectedly, feel shaky, have a faster heartbeat, or feel anxious.
Hyperthyroidism can cause increased sweating and heat intolerance.
Night sweating is not enough to diagnose thyroid disease, but it can be part of a larger pattern.
Possible clues include:
Feeling hot when others are comfortable.
Unexplained weight loss.
Fast heartbeat.
Tremor.
Anxiety.
Frequent bowel movements.
Fatigue.
Sleep difficulty.
Sweating more than usual.
In this case, sweating is linked to internal metabolic heat and nervous system activation.
Medications Can Trigger Night Sweats
Some medications can increase sweating.
Examples may include certain antidepressants, hormone therapies, medications used for diabetes that can contribute to low blood sugar, fever-reducing medicines, some pain medicines, and other drugs that affect the nervous system, hormones, or temperature regulation.
Medication-related night sweating can be confusing because it may start after a new prescription, a dose change, or a change in timing.
Do not stop prescribed medication on your own.
If night sweats begin after starting or changing a medication, discuss it with a healthcare professional or pharmacist. The solution may involve timing, dose review, switching medication, or checking for another cause.
The important point is that the sweat system can be influenced by chemistry.
Not all night sweats come from the room or the blanket.
Alcohol and Night Sweating
Alcohol can make night sweating more likely.
It can affect blood vessels, sleep architecture, temperature regulation, blood sugar patterns, and breathing during sleep. Some people also sweat during alcohol withdrawal or after heavier drinking.
Alcohol may initially make someone sleepy, but it can fragment sleep later in the night. It can also worsen snoring or sleep-disordered breathing in some people.
The result can be a restless, sweaty night.
If sweating appears mostly after drinking alcohol, the pattern is important.
The body may be responding to alcohol metabolism, sleep disruption, blood vessel changes, or withdrawal-like activation.
Spicy Food and Late Heavy Meals
Spicy foods can trigger sweating in some people.
This is called gustatory sweating when sweating is linked to eating. Spicy meals contain compounds that can activate heat-sensing pathways. If eaten close to bedtime, they may contribute to nighttime warmth, reflux, or sweating in sensitive people.
Heavy meals late at night can also affect sleep.
Digestion requires work. Body temperature, blood flow, glucose, and hormones change after eating. A large meal close to bed may make the body feel warmer or more restless.
This does not mean dinner is dangerous.
It means timing and meal composition can affect sleep comfort.
Sleep Apnea and Breathing Disruption
Sleep apnea can be associated with night sweating in some people.
When breathing repeatedly stops and restarts during sleep, the body may experience stress responses, oxygen changes, and repeated micro-awakenings. This can activate the sympathetic nervous system and contribute to sweating.
Possible signs include:
Loud snoring.
Gasping or choking during sleep.
Pauses in breathing noticed by someone else.
Morning headaches.
Dry mouth on waking.
Daytime sleepiness.
Difficulty concentrating.
Waking unrefreshed.
Night sweating alone does not diagnose sleep apnea.
But night sweats plus snoring, gasping, or daytime sleepiness should not be ignored.
Hyperhidrosis: Sweating More Than Expected
Hyperhidrosis is a condition in which sweating is excessive and unpredictable.
Some people sweat more than expected even when they are not hot or exercising. It can affect the hands, feet, underarms, face, or other areas.
If excessive sweating happens at night without fever, weight loss, medication changes, or other symptoms, hyperhidrosis may be one possible explanation.
But true night sweats that soak clothing or bedding still deserve careful review, especially if they are new or persistent.
The difference matters.
Some people are naturally sweaty.
Others are having a new symptom.
Individual Factors
Night sweating varies from person to person.
Several factors can influence it:
Age.
Hormonal stage.
Room temperature.
Bedding.
Body size.
Fitness level.
Stress.
Alcohol intake.
Caffeine timing.
Medications.
Blood sugar regulation.
Infection.
Thyroid activity.
Sleep apnea risk.
Anxiety level.
Menstrual cycle.
Pregnancy or postpartum state.
Menopause or perimenopause.
The same bedroom temperature can feel comfortable to one person and too hot for another.
The same blanket can be fine in winter and too heavy in spring.
The same dinner can feel normal one night and trigger sweating after a stressful day.
The body is not a machine with one setting.
It adjusts constantly.
Step-by-Step: What Happens Inside Your Body
Step 1 — Your Body Monitors Temperature During Sleep
What the Body Detects
While you sleep, the brain continues monitoring internal temperature.
It receives information from the skin, blood, hormones, immune signals, and nervous system. If the body begins to feel too warm or receives a signal that heat needs to be released, the cooling system prepares to respond.
This can happen because the room is warm.
It can also happen because internal systems are active.
Step 2 — The Brain Activates Cooling Pathways
Which System Becomes Active
The hypothalamus helps coordinate temperature regulation.
When cooling is needed, blood vessels in the skin may widen and sweat glands may activate. Sweat appears on the skin surface.
The goal is evaporation.
The body is trying to release heat and protect internal balance.
Step 3 — Sweat Reaches the Skin
Why You Wake Up Damp
Sweat moves through the sweat glands onto the skin.
If the sweat is light, you may not wake up.
If sweating is heavy, you may wake because your clothes, pillow, or bedding feel wet. The body may feel hot at first, then cold as sweat evaporates and damp fabric cools the skin.
This is why night sweats can produce two opposite sensations:
Heat first.
Chills later.
Step 4 — The Trigger Continues or Stops
Why Some Episodes Pass Quickly
If the trigger was external, such as a heavy blanket, the sweating may improve once you remove the blanket or cool the room.
If the trigger was a hot flash, low blood sugar, fever, medication effect, alcohol, or stress response, the sweating may continue until that internal signal settles.
The duration depends on the mechanism.
Environmental overheating may improve quickly.
Hormonal, metabolic, or medical triggers may repeat.
Step 5 — Sleep Becomes Fragmented
Why Night Sweats Can Make You Tired
Sweating can wake you.
Changing clothes, flipping the pillow, removing blankets, or feeling chilled can interrupt sleep. Even if you fall back asleep quickly, repeated episodes can fragment the night.
This can lead to:
Morning fatigue.
Brain fog.
Irritability.
Daytime sleepiness.
Poor concentration.
More caffeine use.
Sleep disruption becomes part of the problem.
The sweating causes waking.
The waking worsens recovery.
Step 6 — The Pattern Reveals the Cause
What Happens Over Time
One sweaty night after a warm room is usually not the same as repeated drenching sweats in a cool room.
The pattern gives clues.
Ask:
Was the room hot?
Was the bedding heavy?
Did I drink alcohol?
Did I eat spicy food?
Was I stressed?
Did I have fever?
Did I change medication?
Did I wake shaky or hungry?
Do I snore or gasp?
Is this happening often?
The pattern matters more than one isolated episode.
Is This Normal?
Yes, sweating at night can be normal when it happens occasionally and has an obvious explanation.
Common harmless triggers include:
A warm bedroom.
Heavy blankets.
Non-breathable pajamas.
Alcohol.
Spicy food.
Exercise close to bedtime.
Stressful dreams.
Temporary illness.
Hormonal changes.
But night sweats become more important when they are repeated, drenching, unexplained, or disruptive.
It is especially important to pay attention if they happen in a cool room and soak clothes or bedding.
It is also important if they come with other symptoms such as fever, unexplained weight loss, persistent cough, pain, fatigue, swollen lymph nodes, shortness of breath, low blood sugar symptoms, or new medication changes.
Occasional sweating is often simple.
Persistent night sweats are a signal to investigate.
When It May Be Worth Speaking With a Healthcare Professional
Speak with a healthcare professional if night sweats are severe, frequent, new, worsening, or interrupting sleep.
Also seek medical advice if night sweats are associated with:
Fever.
Unexplained weight loss.
Persistent cough.
Chest pain.
Shortness of breath.
Severe fatigue.
Swollen lymph nodes.
Pain.
Drenching sweats that soak clothing or bedding.
Night sweats in a cool room.
Shaking chills.
Fast heartbeat.
Confusion.
Low blood sugar symptoms.
New medication use.
Recent medication dose change.
Symptoms of hyperthyroidism.
Snoring, gasping, or breathing pauses during sleep.
Menopause symptoms that are disrupting sleep or daily life.
This does not mean night sweats automatically indicate something serious.
It means recurring or unexplained sweating should be interpreted properly.
How to Reduce or Manage It
Start With the Sleep Environment
First, remove the obvious heat load.
Try:
A cooler room.
Lighter blankets.
Breathable sheets.
Breathable pajamas.
Better airflow.
A fan if appropriate.
Moisture-wicking sleepwear.
Avoiding heat-trapping mattress toppers.
Keeping pets off the bed if they trap heat.
If sweating improves, the cause may have been environmental.
This is the simplest place to start.
Check Bedding and Pajama Materials
Some fabrics trap heat and moisture.
Synthetic pajamas, heavy fleece, thick comforters, and non-breathable bedding can make sweating worse.
Better options may include breathable cotton, linen, bamboo-based fabrics, lightweight wool, or moisture-wicking sleepwear.
The goal is not only to stay cool.
It is to allow heat and moisture to escape.
Avoid Alcohol Close to Bed
If night sweats happen after drinking alcohol, reduce or avoid alcohol close to bedtime and observe the difference.
Alcohol can disrupt sleep, affect blood vessels, and worsen sweating in some people.
Track the pattern for one to two weeks.
If alcohol is the trigger, the body usually makes it obvious.
Watch Spicy Food and Heavy Late Meals
Spicy food can activate heat and sweating pathways.
Heavy meals close to bedtime can also make the body work harder during the night.
If sweating happens after spicy dinners, late eating, or large meals, test an earlier and lighter dinner.
This is not about strict restriction.
It is about reducing nighttime physiological load.
Review Caffeine Timing
Caffeine can affect sleep quality and nervous system activation.
Even if it does not directly cause sweating, it can make sleep lighter and stress responses more noticeable.
If you sweat at night and sleep poorly, keep caffeine earlier in the day for one to two weeks and observe the difference.
The question is not only whether caffeine keeps you awake.
The question is whether it keeps your body activated.
Track Blood Sugar Clues
If night sweating comes with shakiness, hunger, fast heartbeat, nightmares, morning headache, or confusion, blood sugar may be involved.
This is especially important for people with diabetes, people using glucose-lowering medications, or people with a history of low blood sugar symptoms.
Do not guess.
Discuss the pattern with a healthcare professional.
If you monitor blood glucose for medical reasons, bring your readings and symptom timing to the visit.
Review Medication Changes
Ask:
Did sweating start after a new medication?
Did the dose change?
Did the timing change?
Did I stop a medication recently?
Do not stop prescribed medication without advice.
Instead, speak with your healthcare professional or pharmacist. Medication-related sweating can sometimes be managed by adjusting timing, changing dose, or considering alternatives.
Manage Stress Before Bed
Stress-related sweating often improves when the nervous system has a better landing routine before sleep.
Useful options include:
Lower lights.
Stop work earlier.
Avoid intense arguments before bed.
Use a consistent wind-down routine.
Try calm breathing.
Take a warm shower earlier in the evening.
Write down tomorrow’s tasks.
Keep the phone away from bed.
The goal is to signal safety to the nervous system.
A calm room does not always create a calm body.
The body needs repetition.
Look for Sleep Apnea Signs
If night sweats come with loud snoring, gasping, choking, morning headaches, dry mouth, or daytime sleepiness, sleep apnea should be considered.
This does not mean you can diagnose it yourself.
It means the pattern is worth discussing with a healthcare professional.
Sleep apnea is often missed because people may not remember waking during the night.
A sleeping partner may notice the most important clues.
Track the Pattern for Two Weeks
Track:
Room temperature.
Bedding.
Pajamas.
Alcohol.
Spicy food.
Late meals.
Caffeine timing.
Stress level.
Exercise timing.
Medication changes.
Fever or illness.
Menstrual cycle or hormonal symptoms.
Blood sugar symptoms.
Snoring or gasping.
How wet the clothes or sheets become.
How often it happens.
Patterns are more useful than panic.
A two-week log can help separate environmental sweating from hormonal, metabolic, medication-related, or medical causes.
Common Myths and Mistakes
Myth 1 — Night Sweats Always Mean Something Serious
No.
Many night sweats come from simple causes such as a warm room, heavy blankets, alcohol, spicy food, stress, or temporary illness.
But repeated, drenching, unexplained night sweats should not be ignored.
The balanced view is:
Do not panic.
Do not dismiss the pattern.
Myth 2 — If the Room Is Cool, Sweating Cannot Be From Heat
Not always.
Even in a cool room, bedding or sleepwear can trap heat. A mattress topper, thick comforter, or synthetic pajamas can create a warm microclimate around the body.
The room may be cool.
The bed may not be.
Myth 3 — Night Sweats Are Only a Menopause Problem
Menopause and perimenopause are common causes, but they are not the only ones.
Night sweats can also involve infection, medications, low blood sugar, thyroid activity, anxiety, alcohol, sleep apnea, or other conditions.
The cause depends on the full pattern.
Myth 4 — Sweating Means You Are Burning Fat
No.
Sweating is mainly a cooling mechanism. It does not mean the body is burning significant fat during sleep.
Sweat loss is mostly fluid loss, not fat loss.
A sweaty night is not a fitness achievement.
It is a temperature or nervous system signal.
Myth 5 — You Should Just Sleep With Fewer Blankets and Ignore It
Changing the environment is a good first step.
But if night sweats continue despite a cool room and light bedding, or if they come with fever, weight loss, pain, fatigue, cough, or other symptoms, they deserve medical attention.
The blanket is not always the cause.
Frequently Asked Questions
Why do I sweat at night?
You may sweat at night because your body is trying to cool itself or respond to internal signals such as hormones, stress, fever, low blood sugar, medications, alcohol, thyroid activity, or sleep disruption.
Are night sweats normal?
Occasional night sweats can be normal, especially if the room is warm, bedding is heavy, or you had alcohol, spicy food, stress, or exercise close to bedtime. Repeated or drenching night sweats should be evaluated.
What is the difference between being hot at night and night sweats?
Being hot at night usually improves when you cool the room or remove blankets. Night sweats are more excessive and may soak sleepwear or bedding, sometimes even in a cool environment.
Can anxiety cause night sweats?
Yes. Anxiety and stress can activate the sympathetic nervous system, which can increase sweating, heart rate, and nighttime arousal.
Can low blood sugar cause night sweats?
Yes. Low blood sugar can trigger sweating, shakiness, hunger, anxiety, fast heartbeat, nightmares, or waking suddenly. This is especially important for people with diabetes or people using glucose-lowering medications.
Can medications cause night sweats?
Yes. Some medications can increase sweating, including certain antidepressants, hormone therapies, diabetes medications, pain medicines, and other drugs that affect the nervous system or temperature regulation.
Can menopause cause night sweats?
Yes. Hormonal changes during perimenopause and menopause can trigger hot flashes and night sweats. These can wake the person from sleep and may cause damp clothing or bedding.
Can alcohol cause night sweats?
Yes. Alcohol can affect temperature regulation, blood vessels, sleep quality, and nervous system activity. Some people notice night sweats after drinking, especially close to bedtime.
When should I worry about night sweats?
Speak with a healthcare professional if night sweats are frequent, drenching, unexplained, worsening, or associated with fever, weight loss, cough, pain, swollen lymph nodes, fatigue, shortness of breath, low blood sugar symptoms, or sleep disruption.
How can I reduce sweating at night?
Start with a cooler room, lighter bedding, breathable pajamas, less alcohol near bedtime, earlier lighter dinners, less spicy food, caffeine earlier in the day, stress reduction before bed, and tracking symptoms for patterns.
Final Takeaway
Sweating at night is not one single body message.
Sometimes it is simple overheating.
Sometimes it is a hormonal wave.
Sometimes it is stress, low blood sugar, alcohol, medication, infection, thyroid activity, sleep apnea, or another internal trigger.
Inside the body, night sweating happens when the cooling system turns on during sleep. The brain activates sweat glands, skin blood flow changes, and the body tries to release heat or respond to a stress signal.
The practical lesson is to look for the pattern.
Was the room hot?
Were the blankets heavy?
Did you drink alcohol?
Did you eat spicy food?
Are you stressed?
Did you change medication?
Do you have fever, weight loss, cough, or pain?
Do you wake shaky or hungry?
Do you snore or gasp?
Occasional sweating after an obvious trigger is usually not alarming. But repeated, drenching, unexplained night sweats deserve proper medical evaluation.
Your body is not sweating at night for no reason.
It is trying to regulate something.
Sources and Further Reading
- Cleveland Clinic. “Night Sweats: Menopause, Other Causes & Treatment.”
https://my.clevelandclinic.org/health/symptoms/16562-night-sweats - MedlinePlus Medical Encyclopedia. “Sweating.”
https://medlineplus.gov/ency/article/003218.htm - MedlinePlus. “Menopause.”
https://medlineplus.gov/menopause.html - Mayo Clinic. “Night Sweats: Causes.”
https://www.mayoclinic.org/symptoms/night-sweats/basics/causes/sym-20050768 - Mayo Clinic. “Night Sweats: When to See a Doctor.”
https://www.mayoclinic.org/symptoms/night-sweats/news/sym-20050768?p=1 - Sleep Foundation. “Causes and Tips to Prevent Sweating at Night.”
https://www.sleepfoundation.org/night-sweats - Sleep Foundation. “What Causes Night Sweats?”
https://www.sleepfoundation.org/night-sweats/causes-of-night-sweats - MedlinePlus Medical Encyclopedia. “Low Blood Sugar.”
https://medlineplus.gov/ency/article/000386.htm - MedlinePlus Medical Encyclopedia. “Hyperthyroidism.”
https://medlineplus.gov/ency/article/000356.htm - MedlinePlus Medical Encyclopedia. “Hyperhidrosis.”
https://medlineplus.gov/ency/article/007259.htm