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on the palm (between thumb and index finger) can be due to allergic dermatitis, eczema, contact dermatitis, shingles, psoriasis, fungal infection like Tinea or due to palmar warts, which is a HPV infection. Since it is between two fingers, it can also be scabies. It is difficult to comment beyond this at this stage without examining the rash. Please consult a skin specialist for correct diagnosis and treatment. Take care!