An overview over some of the most commonly used UV filtering ingredients.
Choosing the right sunscreen is not an easy task and depends on a lot of factors. There are several ingredients that can protect the skin from UV radiation. Some of them have raised questions due to health and environmental concerns. However, unprotected prolonged sun exposure causes much more harm than any of the ingredients, especially in places with high UV radiation. Regulations and SPF factors usually assume that people use 2 mg per cm² skin surface. This equals about half a teaspoon for the face and one golfball worth of sunscreen for the whole body. The sunscreen should be applied 15 min before sun exposure.
There are two types of UV radiation causing skin damage. UVB causes sunburn and the SPF measures protection against it. UVA causes more long-term damage and exposure has to be prevented additionally.
Oxybenzone is a very effective chemical UV protectant against both UVA and UVB radiation. However, it is labeled as a likely endocrine disruptor by the EU. Also, it has been banned by Hawaii and Palau due to suspected damage to corals and aquatic life.
Avobenzone, Homosalate, and Octocrylene are chemical UV protectants that have different advantages and disadvantages. Avobenzone is important for UVB protection while the other two only protect against UVA. Homosalate is considered a likely endocrine disruptor by the EU and all of them are suspected to harm aquatic life and coral reefs.
Zinc Oxide and Titanium Dioxide are white mineral pigments that reflect sunlight rather than absorbing it. They can cause white smudges on the skin when applied which is avoided by using them as nano particles. They protect the skin very well both against UVA and UVB radiation. Generally, they give little cause for concern for health or the environment but their nano form may be harmful to corals and aquatic life.
Clothing offer an effective and environmentally friendly alternative for sun protection. There is specifically protective clothing but also a cotton shirt is often sufficient. Generally, the protection is better for denser fabric (synthetic over cotton) and darker colors.
I did my best to accumulate data on the different relevant aspects for each ingredient and identify reliable sources (which is sometimes difficult on this topic). The main sources were the formulator text books, the EU, Hawaiian legislative documents as well as published studies investigating the effect of UV filtering ingredients on corals and aquatic life.