Avobenzone is the only chemical UV-protection component with a broad spectrum coverage. It can help to block both UVA I and UVA II rays. It's safe and it is allowed to use at a 3% concentration in the USA and a 5% concentration in the EU countries.
There is one problem: avobenzone loses efficiency when exposed to the sun. If you are outside, it loses 36% of its ability to block UV rays an hour after application. That's why it's recommended to reapply sunscreen every 2 hours.
BHT is a stabilizer and antioxidant. It helps to keep the product fresh for a long time, preventing the oxidization of components. It is stable even in high temperatures, that’s why it’s an essential component in some products. It also protects the skin from free radicals. As for safety, the component isn't researched very well. It’s considered to be safe in low concentrations. But there is still not enough scientific data collected.
