Common causes of leg rash include allergic reactions, inflammation, infection, autoimmune process, or parasite or insect bites, according to Healthgrades. Other potential causes include varicose veins, heat, stress, methamphetamine abuse or venous eczema, which results from a blood vessel disorder.
A possible cause of a sudden, acute leg rash is an allergic reaction to a specific substance, such as hair wax, poison ivy or a bite from a mosquito, mite, flea, body lice or bedbug, states Healthgrades. Eczema, or atopic dermatitis, and psoriasis are likely causes of a leg rash occurring for a long period. Bumpy, itchy skin with silvery scales and red edges indicates psoriasis.
Infections that can lead to a leg rash include chickenpox, bacterial infection, fungal skin infection, fifth disease and folliculitis, in which the hair follicle becomes infected or inflamed, says Healthgrades. A drug reaction; allergic purpura, which causes a rash of purple patches; and allergic contact dermatitis are allergic conditions that cause a leg rash.
A leg rash is sometimes a symptom of a severe condition, such as a serious allergic reaction known as anaphylaxis, in which the body's airways tighten and close, notes Healthgrades. Anyone who experiences accompanying symptoms such as wheezing, shortness of breath, or a swollen mouth, throat or face should seek prompt medical treatment.