Dear Doctor,

Is it normal for my teenage daughter not to sweat at all? Even when she runs around, or on a very hot day, she doesn’t sweat. Why is this?  Faith -----

Dear Faith,

Sweat is produced by sweat glands in the body and the main function is to regulate body temperature, keeping it cool.  Absence of sweating may be partial, that is, part of the body may not sweat. This can be ignored. But total lack of sweating is not normal and needs investigations to exclude a preventable or treatable cause. 

Lack of sweating (anhidrosis) can be due to absence of sweat glands since birth. Damage to the skin as due to burns or radiation injury can affect the sweat glands resulting in reduced or absent sweating. Inherited conditions that affect the metabolism like Fabry disease can also cause absence of sweating.  It can be due to connective tissue disorders like Sjögren’s syndrome, where along with lack of sweating, there is dry eyes and mouth. Disorders that affect the autonomic nervous system like diabetes mellitus, alcoholism, Guillain-Barré syndrome, can affect the sweat glands and manifest as absence of sweat. 

Psoriasis, an autoimmune disorder that affects the skin predominantly, tends to clog the sweat pores, resulting in absence of sweat. It can be due to drugs like morphine and some antipsychotic medications.

Whatever the reason for lack of sweating, it makes one vulnerable to heat stroke and hyperthermia on exposure to heat. This can manifest as dizziness, muscle cramps, dryness of mouth, fever, dehydration and electrolyte imbalance.

One having anhidrosis should take measures to avoid a sunstroke. This includes wearing loose comfortable clothes during hot weather, avoiding going out when it is hot, drinking more water and taking hydrating drinks like lemonade, avoiding physical overexertion, using cool spray over the body, and etcetera. Most importantly, one should recognise signs of heat stroke and take treatment at the earliest time. Diagnosis of anhidrosis can be made by history and physical examination. Further tests can be done to confirm it and one of them is a sweat test. 

During this test, one is coated with a powder that changes colour when and where the person sweats.  The person then enters a chamber that causes 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. In some cases, the doctor might request a biopsy of the area suspected of anhidrosis. For this test, skin cells and sometimes sweat glands are removed for examin ation under a microscope. Treatment depends on underlying cause.                                                           

                                  Dr.Rachna   Pande is a specialist in internal medicine.