Anhidrosis is the inability to sweat normally. When you don't sweat (perspire), your body can't cool itself, which can lead to overheating and sometimes to heatstroke — a potentially fatal condition.

Anhidrosis — sometimes called hypohidrosis — can be difficult to diagnose. Mild anhidrosis often goes unrecognized. Dozens of factors can cause the condition, including skin trauma and certain diseases and medications. You can inherit anhidrosis or develop it later in life.

Treatment of anhidrosis involves addressing the underlying cause, if one can be found.

Signs and symptoms of anhidrosis include:

• Little or no perspiration
• Dizziness
• Muscle cramps or weakness
• Flushing
• Feeling hot

A lack of perspiration can occur:

• Over most of your body (generalized)
• In a single area
• In scattered patches

Areas that can sweat may try to produce more perspiration, so it's possible to sweat profusely on one part of your body and very little or not at all on another. Anhidrosis that affects a large portion of your body prevents proper cooling, so vigorous exercise, hard physical work and hot weather can cause heat cramps, heat exhaustion or even heatstroke.

Anhidrosis can develop on its own or as one of several signs and symptoms of another condition, such as diabetes or skin injury.

When to see a doctor

If you barely sweat, even when it's hot or you're working or exercising strenuously, talk to your doctor. Talk to your doctor if you notice you're sweating less than usual.

Seek immediate medical attention if you develop signs or symptoms of heatstroke.

Anhidrosis occurs when your sweat glands don't function properly, either as a result of a condition you're born with (congenital condition) or one that affects your nerves or skin. Dehydration also can cause anhidrosis. Sometimes the cause of anhidrosis can't be found.

Causes of anhidrosis include:

• Conditions you're born with, such as certain congenital dysplasias that affect the development of sweat glands
• Inherited conditions that affect your metabolic system, such as Fabry's disease
• Connective tissue diseases, such as Sjogren's syndrome, which causes dry eyes and mouth
• Skin damage, such as from burns or radiation therapy, or diseases that clog your pores (poral occlusion), such as psoriasis
• Conditions that cause nerve damage (neuropathy), such as diabetes, alcoholism and Guillain-Barre syndrome
• Certain drugs, such as morphine and botulinum toxin type A, and those used to treat psychosis

Heat-related illnesses are the most serious complications of anhidrosis. Children are especially vulnerable because their core temperatures rise faster than adults', and their bodies release heat less efficiently.

Heat-related problems include:

• Heat cramps. Symptoms include muscle pain or spasms. Rest in a cool place and drink water or a sports drink. Get medical help if cramps last longer than an hour.
• Heat exhaustion. Signs and symptoms include weakness, nausea and a rapid pulse. Move to a cool place and get medical help if symptoms last longer than an hour.
• Heatstroke. This life-threatening condition occurs when your body temperature reaches 103 F (39.5 C) or higher. Skin may be hot, red or dry. If not treated immediately, heatstroke can cause loss of consciousness.

Anhidrosis often can't be prevented, but serious heat-related illnesses can. To stay safe:

• Wear loose, light clothing when it's warm.
• Stay cool indoors on hot days.
• Use a spray bottle containing water to cool yourself.
• Monitor your activity level closely so you don't overdo it.
• Learn the signs of heat-related illness and how to treat them.

Your doctor is likely to suspect anhidrosis based on your signs and symptoms, your medical history, and a physical exam. But you may need certain tests to confirm the diagnosis. These include:

• Sweat test. During this test, known as a thermoregulatory sweat test, you're coated with a powder that changes color when and where you sweat. You then enter a chamber that causes your body temperature to increase to a level that makes most people perspire. Digital photos document the results, and the whole body surface can be tested at once.
• Skin biopsy. In some cases, your doctor might request a biopsy of the area suspected of anhidrosis. For this test, skin cells and sometimes sweat glands are removed for examination under a microscope.

Anhidrosis that affects a small part of your body usually isn't a problem and doesn't need treatment. But large areas of decreased perspiration can be life-threatening. Treatments may depend on the condition that's causing the anhidrosis. For example, if medications are causing the condition, discontinue taking that drug, if possible. If clogged sweat ducts are causing the condition, cleaning the skin with a gentle exfoliant might help.

You're likely to start by seeing your family doctor or a general practitioner. You may then be referred to a doctor who specializes in skin disorders (dermatologist).

Here's information to help you get ready for your appointment.

What you can do

• Be aware of pre-appointment restrictions. When you make the appointment, ask if you need to do anything to prepare, such as modifying your diet.
• Write down your symptoms, including ones that seem unrelated to your reason for scheduling an appointment.
• Write down key personal information, including major stresses or recent life changes.
• List all medications, vitamins and supplements you take.
• Ask a family member or friend to come with you to help you remember information you're given.
• Write down questions to ask your doctor.

Preparing a list of questions can help you make the most of your time with your doctor. For anhidrosis, some basic questions to ask your doctor include:

• Why don't certain parts of my body sweat?
• What tests do I need?
• What caused this condition?
• Will I always have this condition?
• What treatments are available, and which do you recommend?
• How can I best manage this condition with my other health conditions?
• Should I restrict activities?
• Do you have any brochures or other printed material for me? What websites do you recommend?

Don't hesitate to ask other questions, as well.

What to expect from your doctor

Your doctor is likely to ask you a number of questions, including:

• When did you notice you weren't sweating?
• What parts of your body don't perspire?
• Are you aware of others in your family with similar symptoms?
• Do you have other symptoms?
• Does anything seem to improve your symptoms?
• What, if anything, appears to worsen your symptoms?
• Did symptoms begin when you changed a medication or were diagnosed with another illness?