Palau’s strict environmental measures and ban on sun cream harmful to corals and sea life took effect on Wednesday.
Sun cream containing common ingredients, including oxybenzone, are not allowed to be worn or sold in the country from now on, reports BBC.
Palau, located east of the Philippines and north of Indonesia, has an economy that relies on tourism and fishing.
The island nation markets itself as a "pristine paradise" for divers who admire the coral reefs so much that they have dubbed them the underwater Serengeti.
A lagoon in Palau's Rock Islands is a Unesco World Heritage site. The country has a population of around 20,000 dotted across hundreds of islands.
The ban - which was announced in 2018 - prohibits sun cream containing any of 10 harmful ingredients. The list includes oxybenzone and octinoxate, which absorb ultraviolet light.
The International Coral Reef Foundation said the banned chemicals were "known environmental pollutants - most of them are... incredibly toxic to juvenile stages of many wildlife species".
The number of sun creams containing the harmful chemicals is declining. In 2018, experts said it was found in about half of creams and lotions.
When Hawaii announced a similar ban - which comes into effect in 2021 - major brands were quick to say their products were "reef bill compliant".
Other places to announce bans include the US Virgin Islands - where the law takes effect in March - and the Dutch Caribbean island of Bonaire.
Scientists have found that some chemicals in sunscreen can be toxic to coral reefs, which are a vital part of the ocean ecosystem as well as a popular draw for tourists.
But some critics say there are not enough independent scientific studies on the issue while others worry that people will suffer from too much sun exposure if they stop using the products, according to AP.
Some manufacturers, meanwhile, have already started selling “reef-friendly” sunscreen.