Skin mites are potentially harmful; it depends on the mite population on your skin.
As long as the number of mites on your skin remains under control, you're unlikely to experience any problems. However, if too many mites burrow into your skin, it can lead to demodicosis, an infection that causes skin inflammation (04-May-2023).
Therefore, the harm caused by skin mites depends on whether their population is kept under control or not.