Dear Doctor,

I recently developed a rash on my thigh and it has really gotten me scared. What could be the problem? Mugisha

Dear Mugisha,

Is the rash increasing in size, is it crusty, powdery, does it itch? Most common cause for a thigh rash is a fungal infection. Dampness, caused due to sweat, moist underwear, is the risk factor for fungal infection. It is aggravated by nylon under garments. The rash is mostly , whitish or reddish, itchy and grows progressively. It may subside spontaneously to reappear again. Diabetes, HIV and other immune deficient conditions increase susceptibility to a fungal infection.

The rash if itchy, crusty and powdery could be due to psoriasis, a condition said to be due to the immune system considering body’s antigens as foreign. But in this disorder, similar rashes appear on backside of limbs as well as trunk.

Eczema can cause a localized rash due to allergy to something used or prevailing in the atmosphere or eaten. Drugs like pain killers can cause a fixed non pruritic rash(fixed drug reaction) as manifestation of allergy, which may persist for weeks to months. A rash of acute onset can be due to insect bite.

If a very dry skin is rubbed or scratched anywhere, it can result in a temporary rash. If the rash is persistent, it would be prudent to visit a skin specialist.