Sargassum smell and health

Why it smells

Fresh sargassum, the kind floating in the water, barely smells. The smell comes when it piles up on the sand and starts to decay, especially in the heat. As it rots it gives off gases, among them hydrogen sulfide, which causes the rotten-egg smell, and also ammonia. The more sargassum there is and the longer it sits on the sand, the stronger the smell usually gets.

Who it can affect

For most people on a normal beach visit, the smell is unpleasant but causes no harm. Even so, breathing these gases for a while, or in spots with heavy build-up and little wind, can irritate the eyes, nose or throat and cause headaches or nausea in some people.

Take more care if you:

• have asthma or another respiratory condition;
• are pregnant;
• are with babies, young children or older adults;
• feel unwell every time you get close to the seaweed.

This guide is not medical advice. If you have symptoms that do not go away once you move off, see a health professional. In an emergency, call 911.

What to do

• Stay away from large piles of rotting sargassum, especially when there is no breeze.
• Pick another beach if yours has a lot of sargassum piled up. There is almost always another one nearby in better shape.
• Do not touch rotting sargassum with your hands, and do not let children play with it.
• Watch your dog: it should not eat it or roll in it.
• Follow official notices. The Florida Department of Health and the counties publish advice when there are large accumulations. They take priority over anything you read here.

What our index measures

Our index tells you how much sargassum there is on each beach; it does not measure gases in the air. A high level often comes with more smell, especially when it lasts several days, but it is not an air-quality reading. If the smell worries you, the best use of the index is to pick a beach marked "Clean" and read today's reports, where people who are there say what they notice.