Itchy hands with small blisters on hot days may be caused by sweat herpes, tinea versicolor, eczema and other reasons. 1. sweating herpes: the main manifestation of the hand appeared rice-like size blisters, slightly higher out of the skin, more than one or groups of people, around the redness is not obvious, often both sides of the hands and feet symmetrical distribution, itching obvious. 2. ringworm: generally occurs in unilateral hand, is caused by fungal infection, often manifested as small blisters under the skin, blister liquid clarification, to be dry after the blisters flaking skin, accompanied by itching. 3. Eczema: because the hands are easy to sweat in summer, it is easy to induce eczema attacks, red spots, pimples, blisters and other lesions, accompanied by itching. If the symptoms of itchy hands with small blisters on hot days, you need to go to the hospital as soon as possible, by the doctor according to the specific conditions, to develop individualized diagnosis and treatment plan, so as not to delay the condition.