If you have a problem with the tone of your skin, then it is likely caused by an issue with the melanin. Melanin gives your skin its pigment, or colour. Hyperpigmentation, for example, is a condition where your body produces too much melanin and your skin gets darker in some areas. Hypopigmentation, on the other hand, is a condition where you body does not produce enough melanin, and your skin gets lighter in some areas. Learning the cause can help you reverse these issues with melanin.
Visit your doctor. There are certain medical conditions which can cause issues with melanin production. A skin infection, for example, can cause hypopigmentation, while a disorder known as Addison's disease can cause hyperpigmentation. Your doctor can diagnose such problems and prescribe a course of treatment.
Use any prescription cream that your doctor prescribes to reverse the melanin issue. For example, melasma, a condition that causes hyperpigmentation, can be reversed with a prescription cream. A skin infection or severe burns and blisters might require a prescription to reverse the issue with your melanin production.
Limit the time you spend in the sun. Over exposure to the sun can cause melanin production problems. If you do get sun exposure, use a sunscreen with an SPF of 30 or more.
Note that pregnancy can cause hyperpigmentation of the skin. In this case, the melanin issue will likely dissipate once you have the baby and your hormones become balanced.