Why is my skin darkening around the mouth after chemical peel? (photo)

There may be some post inflammatory pigmentation developing in that area. Consult with the physician who treated you. There are several options available to prevent progression of this process and to treat your skin during this healing period.

The area of skin around the mouth
tends to be a little more sensitive. So depending on peel technique and the
strength of the peel, some darkening can happen. We would recommend light
gentle moisturizers for an extended period of time as well as hydroquinone for
night time and of course sunscreen every morning.