Eczema is thought to be caused by the body's excessive immune response to an irritant, although the exact cause is unknown, according to WebMD. There may be a genetic component to eczema, since it tends to show up in families that also have high frequencies of allergies or asthma.
Individual attacks of itching from eczema are often brought on by skin contact with course or rough materials, WebMD says. Other causes are temperature extremes, exposure to household cleaners including soap or contact with pets. Colds, flus and stress can increase a person's sensitivity and likelihood of an eczema flare-up. There is no cure for eczema, but medications and avoiding known irritants can minimize the symptoms. Common medications include hydrocortizone creams, other creams, ointments and oral medications.
Itching is the most consistent symptom of eczema, according to WebMD. Itching can occur before a rash appears, and when it does the rash most often shows up on the back of the knees, feet, wrists, hands or face. The rash can manifest as a scaly, dry or thickened area on the skin. People with naturally darker skin can also have the affected areas become lighter or darker. Infants can develop oozing rashes that both cause itching and can crust over.