Humans and marine life experience adverse health effects from sargassum build up. Decaying seaweed produces large amounts of toxic gas, including hydrogen sulfide (H₂S) and ammonia (NH3).

Prolonged exposure to high concentrations of hydrogen sulfide gas can also cause human health problems including nausea, headaches, skin rash and even breathing difficulties) .

Marine life is also adversely impacted by hydrogen sulfide that’s released into the water by rotting sargassum. It is toxic to aquatic animals because it interferes with reoxidation of cytochrome a3 in respiration. In 2018 scientists began to register a rising death toll of marine species - fish, crustaceans, octopuses, sea cucumbers - in zones with high sargassum concentrations on the beaches. Corpses of 78 different species were found in the accumulated sargassum along the beaches of Quintana Roo.

Hydrogen sulfide even corrodes sensitive electronic appliances such as TVs, computers, and air-conditioning units.