Why Does Sitting On My Leather Chair Cause A Red, Itchy Rash On My Thighs That Lasts For Days?

When I sit on my leather chair. I get red lines and red flat bumps. I ve tried wearing multiple layers of clothes and covering it and right now it s covered with thick blanket and it still causes rash on the back of my thighs and the side of my thighs. It occurs after about 1-2 hours and progressively gets worse. By the time I m done, hours later my whole thigh is red and itching that lasts for usually two days if I stay out of the chair. I ve tried cleaning it as well. I think it s bonded leather. I have two fabric chairs and they don t make me itch.