A rash that only appears on the lower legs can be caused by vasculitis, venous eczema, cellulitis or dermatitis, according to Healthgrades. Atopic dermatitis, or eczema, and molluscum contagiosum also cause rashes, mostly on the lower legs of children, adds Parents.
Atopic dermatitis occurs because the skin doesn't retain moisture like it should and becomes dry and cracked, often flaring up when exposed to excessive heat, harsh chemicals in soaps and lotions, and wool, explains Parents. It generally occurs behind the knees. Molluscum contagiosum occurs primarily on the lower legs, also in children, because of a viral infection, but it naturally resolves itself.
Venous eczema, also known as stasis dermatitis, occurs when blood pools in veins in the legs due to blood vessel damage, leg trauma or deep vein thrombosis, states Healthline. This pooling blood makes a rash appear just under the skin and can be accompanied by swelling, tenderness, pain and itchiness. Leg ulcers and seepage can result if the condition isn't treated.
Vasculitis, the inflammation of blood vessels in the legs, also causes a rash, Mayo Clinic reports. Because it has so many causes, treatment depends on the cause. Corticosteroids can help to reduce blood vessel inflammation and provide some relief.