It sounds like you have developed some type of dermatitis in between the fingers. Dermatitis is just a generic term that describes inflammation of the skin. In your case, if you don't know if you were exposed to anything that could have caused this, then it could be classified as atopic dermatitis. The treatment for this is various different moisturizing creams and steroid creams during flairs. Atopic dermatitis does not typically only effect the area in between the fingers (but certainly could). In fact, it usually effects the area on the inside of the elbow and causes itching that gets worse when scratched.
Another (much less likely) possibility is that this area of irritation is an infection with the skin mite scabies. Scabies is a parasite that boroughs into the skin and causes intense itching. It happens to really like the area in between the fingers. Your skin being red and irritated is not typical of scabies, unless you have scratched this area raw causing it to look like an open cut.
I suggest that you schedule an appointment with a dermatologist
. He or she can examine the area of irritation in between your fingers, figure out what it is, and prescribe the appropriate treatment. Good luck.