The answer to your question will depend largely on what precisely is the cause of the spots. In order to figure this out, however, you will need to go see your primary care doctor
, as a physical examination by your doctor is the only way to get a firm diagnosis.
One possibility is that these spots represent a fungal infection. There is a type of fungal infection of the skin called tinea versicolor which tends to cause light-colored patches, often on the chest and back, which can sometimes be a bit itchy. They tend to clear up with topical anti-fungal medications, which your doctor will be able to give you if the diagnosis is confirmed.
Another possibility is an inflammatory condition of the skin, such as eczema
or a contact dermatitis. These patches or spots tend to be itchier than those caused by a fungal infection, and the treatment for them is different from the treatment for fungal infections of the skin. Most will clear up with topical steroid creams as well as avoiding contact with the offending agent, if one is identified.
Start by calling your primary care doctor's office and making an appointment at your earliest convenience.