Sunburn and heat prostration are concerns, even in winter. So hit the beach or play tennis, golf, or another outdoor sport before 10 am or after 3 pm. If you must be out at midday, limit exercise, drink plenty of nonalcoholic liquids, and wear both sunscreen and a hat. If you feel faint, get out of the sun and sip water slowly.
Even on overcast days, ultraviolet rays shine through the haze, so use a sunscreen with an SPF of at least 15, and have children wear a waterproof SPF 30 or higher.
While you're frolicking on the beach, steer clear of what look like blue bubbles on the sand. These are Portuguese men-of-war, and their tentacles can cause an allergic reaction. Also be careful of other large jellyfish, some of which can sting.
If you walk across a grassy area on the way to the beach, you'll probably encounter the tiny, light-brown, incredibly prickly sand spurs. If you get stuck with one, just pull it out.