Hi,
This could be an allergy or a fungal infection of the foot. Tinea Pedis is a parasitic fungal infection of the epidermis of the human foot.
Several different fungi, called dermatophytes, can cause tinea pedis. It causes scaling, flaking and itching of the affected skin. Blisters and cracked skin may also occur.
It is typically transmitted in moist environments where people walk barefoot, such as showers, bath houses, and locker rooms. It can also be transmitted by sharing footwear with an infected person.
Hygiene therefore plays an important role in managing an athlete's foot infection. Since fungi thrive in moist environments, it is very important to keep feet and footwear as dry as possible. Try to limit the amount that your feet sweat by wearing open-toed shoes or well-ventilated shoes and wear lightweight cotton socks.Use foot powder to help reduce moisture and friction.
The fungal infection is often treated with topical antifungal agents, which can take the form of a spray, powder, cream, or gel. The most common ingredients in over-the-counter products are miconazole nitrate (2%) and tolnaftate (1%). Terbinafine(Lamisil) can also be used.
You can try anti-histamines if it is an allergic rash.
ref:http://en.wikipedia.org/wiki/Tinea_pedis