Selsun Blue is a medicated shampoo that contains the active ingredient selenium sulfide. This bright blue strong-smelling shampoo is used to treat several skin disorders. It is intended for topical use only and should be shaken to thoroughly mix the chemicals prior to application.

Selsun Blue is commonly used to treat an infection of the scalp known as seborrheic dermatitis. This condition causes scaling and itchy red skin on the scalp and can sometimes spread to the upper back, upper chest, face, or other oily areas, according to the Mayo Clinic website.

This harmless but uncomfortable and unsightly condition is caused by yeast growing on oily areas of the skin and combining with bacteria. Stress and fatigue can also promote the condition, which is typically more common in the winter. Those with AIDS or Parkinson disease have a higher risk of developing seborrheic dermatitis.

Medicated shampoos that contain selenium sulfide, such as Selsun Blue, are the first recommended treatment for seborrheic dermatitis. Other shampoos that contain tar, ketoconazole, or pyrithione zinc are also effective. Unfortunately, this shampoo may not eliminate the condition, depending on the condition's severity and the patient's skin type.

Dandruff is the most common reason people buy Selsun Blue. Selenium sulfide is a common treatment for dandruff, which may merely be a side effect of seborrheic dermatitis.

Dandruff is the white, flaky skin shed by the scalp. It's often visible on dark clothing and can be embarrassing. Applying Selsun Blue about twice a week may control this common symptom of another problem.

Dandruff is often caused by dry skin or a lack of shampooing, which allows oil to build up on the scalp and cause flaking. It can also be a side effect of eczema, sensitivity to hair care products, or a yeast infection of the scalp.

Tinea versicolor is a fungal infection of the skin that occurs most often in teenagers and young adults. The fungus disrupts the normal activity of the pigment in the skin, causing patchy discoloring in the skin.

Oily skin, excessive sweating, hormonal changes, and humid climate encourage tinea versicolor. Selsun Blue may be appropriate for mild cases. To treat tinea versicolor, rub the shampoo into a lather over the affected skin and leave it on for 10 minutes before rinsing.

More severe cases may not respond to Selsun Blue and may require more potent topical or oral medication.