When my skin is scratched by anything, it turns red and welts up. what can i do or take to prevent this?

Dermatographia: It sounds like you may have a condition known as dermatographia (literally "skin-writing"). In this condition, any little scratch can cause a local allergic reaction, which is the red welt you are seeing. If this is correct, it is often treated with antihistamines or topical steroids. You should be evaluated by a dermatologist or allergist.