The main safety concerns on the island include the sun, the water, the mosquitoes and the roads.

Be sure to use plenty of sunscreen throughout the day to avoid getting sunburned.  Snorkelers should be particularly careful to reapply sunscreen before each trip into the water, as your back and neck will be continually exposed to the sun even though you may not feel its heat under the water. 

Familiarize yourself with basic water safety guidelines, as most of the activities here take place on or in the ocean.   Parents should be particularly watchful of children.  Guides leading snorkeling, fishing and boating tours can help you with any safety concerns.  If you go out on the water on your own without a guide, be mindful of other boats traveling across the water, especially when snorkeling or kayaking.  Also be aware that the ocean near the shore is very shallow and home to stingrays and coral formations, so it is advisable to avoid walking off the beach into the ocean in order to prevent injury to yourself or the bottom-dwelling marine life.

Around sunset, the mosquitoes come out.  Bug bites can be avoided by liberally using bug spray.  You can bring your own, and it's also readily available at resorts and shops.

Finally, although there aren't many cars on the island, the streets of San Pedro town are heavily used by golf carts, bicyclists, airport taxis and pedestrians.  If you decide to rent a golf cart or bike, be prepared to concentrate on sharing the road rather than sightseeing as you drive through San Pedro.  Outside of town, you'll have the road mostly to yourself.