I often perform test spots to determine how high the tendency is for a patient of skin of color to develop post inflammatory hyperpigmentation (darkening) after Fraxel.If there is significant darkening in a test area, then that patient is not considered a candidate for the procedure, usually. It is important to know that if there is no sign of darkening in the test areas it does not guarantee that it wouldn't happen in the face after a full treatment. There are often topical products that dermatologists have their patients use before and after the procedure to minimize the chance of pigmentation and the regular use of sunscreen and sun protection techniques is crucial.
The risk of darkening can increase in those women who take female hormones and those who are pregnant.
Make sure you listen to the instructions of your doctor.
The information provided in Dr. Shelton's answer is for educational purposes only and is not intended to constitute medical advice. The information provided should not be relied upon as a substitute for consultations with a qualified health professional who may be familiar with your individual medical needs.
Web reference: http://www.thenyac.com/fraxel/index.html