Eczema, dermatitis or fungal infections often cause rashes behind the ears, according to ZocDoc. The area behind the ears is prone to rashes because it tends to be moist.
An eczema rash behind the ears typically has dry, scaly skin and gets worse in cold weather. Use of a moisturizer or steroid cream can treat this rash. Exposure to an irritant typically causes contact dermatitis; removing the irritant usually makes this type of rash disappear, as ZocDoc explains. Dandruff shampoos or steroid creams can treat seborrheic dermatitis, which manifests with large areas of inflammation, often at the hairline. Fungal infections tend to be red, scaly and itchy and are treated with antifungal creams.