Can red light therapy lead to skin cancer?

No, there are neither such theories nor findings about red light therapy. It is the UV light that the sun gives us that may have increased the risk of skin cancer, and those wavelengths are missing in red light therapy, but are found, for example, in solariums. That is why the radiation protection authority has rules about how tanning beds should be used. The red lamps used in red light therapy are classified as ordinary lamps and are usually not medically classified either.