I had a neighbor who had something that looked similar. It just looked like dark skin in the area she would have a mustache, except it wasn't hair it was darkened skin. A dermatologist said it was a type of fungus and treated it with a cream.
If you have a lot of skin issues be aware this may point to food problems and/or digestive tract problems. These problems show up in the skin. If you also get terrible mouth ulcers, that also points to a digestive issue, including Celiac disease or colitis.