I recommend that you go to see either your primary care doctor
or a dermatologist
for a definitive diagnosis of this condition.
When they examine you, your doctor will consider several different potential causes of lightening of the skin.
One of the most likely is something called tinea versicolor, which is a fungal infection of the skin. The condition is very common and it tends to cause patches of lighter colored skin that frequently cluster on the torso. Fortunately, if you are diagnosed, the condition is very easy to treat with simple anti fungal creams that your doctor can prescribe for you!
If you have had trouble with acne
, eczema, or another inflammatory condition of the skin, then these patches might represent areas of post inflammatory hypo pigmentation. This is a condition in which, as part of the healing process in the skin after an injury, the skin pigmentation ends up being lightened away. Fortunately, in most cases of post inflammatory hypo pigmentation, the skin coloration will tend to come back over a period of weeks to months.
Start by setting up an appointment with your doctor at your earliest convenience, so that they can figure out what is going on and get you started on a treatment!