hi. I've had these dark patches on my right armpit for a few months. I recently noticed my chest also starting to get darker patches. They are a few mm to a centimeter in diameteŕ. I am fair skinned. They don't feel any different to my normal skin. I have no pain or itchiness or any symptoms from them. I only noticed them when looking in the mirror. What do you think it is? Thank you very much for reading.