Hi Looks like you have an allergic reaction or an eczematous patch behind your knee. Such lesions are more irritation in nature though less harmful. First you have to avoid touching the area too much and avoid itching. Continous itching tends to increase the eczematous changes and increases the lesion. You can apply some topical moisturizer or oil over the affected area daily. This will tend to reduce the itching sensation. Also you will need to use some topical steroid cream to heal the lesion completely. Take oral antihistamines along if the itching is unbearable. Hope it helps Dr Geetika Paul