A rash on the leg can be caused by parasites, insects, bacterial and viral infections, autoimmune disorders and allergies, according to Healthgrades. People may also experience sporadic leg rashes with excessive stress, anxiety, heat rash, varicose veins, the use of methamphetamines and eczema resulting from deep vein thrombosis.
Serious cases of leg rash may indicate a person is suffering from an underlying health condition, such as diabetes or peripheral artery disease, notes Healthgrades. Some leg rashes are triggered by allergic reactions when skin comes in contact with perfumes and other irritating chemicals. This type of rash is considered a medical emergency if a person shows accompanying signs of anaphylaxis.
It is also possible for people to experience severe allergic reactions to certain medications, which may cause their skin to peel off and their mucous membranes to malfunction. This condition is life-threatening and can result in sepsis, respiratory failure and gastrointestinal hemorrhaging, according to Medscape.
Additional causes of leg rashes include psoriasis, atopic dermatitis, measles, chickenpox, folliculitis, vasculitis, body lice, bedbugs, erythema nodosum and mites, explains Healthgrades. If a leg rash is accompanied by intense itching, it is best not to scratch the area if possible, as this can cause the skin to break open and potentially lead bacteria or fungi to enter the sores and create an infection.