In the majority of cases of lower leg rashes, the root cause is some form of dermatitis, according to DermNet NZ. Dermatitis has symptoms including both bumpy rashes and itchy red marks, as well as thickened plaques. This term is interchangeable with eczema.
There are several types of dermatitis that present on the legs, but three of them most commonly have red bumps or rashes. These are atopic dermatitis, discoid eczema and contact dermatitis, according to DermNet NZ.
Atopic dermatitis presents itself most commonly in children and infants. In typical cases it is found near the ankle and base of the foot, but it is possible to creep up the leg, according to DermNet NZ. In adult cases, it is found behind the knee, and in all cases it is accompanied by intense itchiness.
Discoid eczema is also known as nummular dermatitis, and it is found in humans of any age. This disease presents itself as red, hard plaques throughout the leg, according to DermNet NZ. The most common cause of this problem is overly dry skin or other skin trauma, such as insect bites.
Contact dermatitis is caused by some type of skin irritant, either hygiene product, tight clothing, excessive bathing or allergic reactions. This type of dermatitis looks like a large red blister, according to DermNet NZ.