Hello,
It can be due to pompholyx. The exact cause is not known and excessive sweating can be one of the reasons. But some triggers like allergic reaction to soaps, detergents, foods, latex, nickel etc may trigger the symptoms. Apply some calamine lotion on the affected area and keep the area well moisturized. Use only thin applications of moisturizer ointments as excessive amounts of ointment may restrict breathing of the skin and aggravate the condition.
Topical steroids can be applied but they are available under prescription. Moreover to prevent infection, topical antibiotics may be needed. I suggest you to consult a dermatologist and get it evaluated.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your dermatologist. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Does it itch? Do you notice if it gets worse in stressful times? Could be any of the 3 you mentioned- an allergy, a skin eruption due to stress, all of which of course have to do with your immunity and nervous system. But the only way to know for sure is a trip to the doc's. In the meantime try aloe vera lotion. It works wonders on all sorts of skin ailments.