While self-tanning is generally considered safe, there are a few things to consider when using DHA. First, there have been few DHA safety studies and this Harvard article concludes that long-term effects remain largely unknown. That being said, one study found that DHA damaged skin cells' DNA, which suggests that more research is needed before DHA can be declared safe for long-term use. DHA is currently [FDA] approved for external use only, excluding the lips, eyes, ears, nose and mucous membranes. Learn more here.