It happens in response to allergens.
Eczema can affect neck, knees, and
elbows and causes oozing, bleeding blisters and thick patches caused by climate, allergens and illness.Psoraisis is characterized with the presence of thick red itchy plaques with white scales on the scalp, elbows, knees, lower back. The cause is possibly hereditary. These are a few possibilities based on the information provided by you. It is very difficult to confirm anything without external examination.