Can a beach trip to Florida’s Gulf Coast make you sick? What the red tide experts say

Florida’s coastal blooms of red tide algae are notorious for triggering immediate allergy-like symptoms that can ruin a day at the beach.

Why does this happen?

The organism that causes red tide, Karenia brevis, produces a powerful toxin that is responsible for irritating our eyes, throat and lungs.

For most people, symptoms of red tide exposure go away shortly after leaving the affected area.

But respiratory irritation is just one potential impact of red tide on human health. Scientists are beginning to explore the other ways that red tide’s toxins can affect us, including new evidence linking red tide exposure to neurological illness.

The many unknowns about red toxins are a good reason to exercise caution and avoid exposure when possible, said Michael Mullan, executive director of the Roskamp Institute in Sarasota, which is studying red tide’s impacts on brain health.

“Until we know that we can be exposed to it at high levels and it doesn’t do any long-term harm, and whether that’s true for everybody, nature is giving us a big signal here,” Mullan said. “There’s an awful lot of dead animals here during these events.”

Here’s what we know about red tide’s health effects and how to avoid them.

What is red tide and how is it harmful?

Toxin: Red tide produces a tasteless, odorless toxin called brevotoxin. In addition to causing upper respiratory irritation, it is capable of crossing the blood-brain barrier and disrupting nervous system processes.

Marine life: In fish and other marine life, this often results in death.

Human health: In humans, it can cause temporary neurological symptoms including nausea, vomiting, diarrhea, numbness and tingling, dizziness, headache and a reversal of hot and cold sensations, a Roskamp Institute study published in August found. “Even healthy folks can get neurological symptoms during a red tide if they get exposed to really high levels,” Mullan said. Swimming in water where red tide is present can irritate skin.

What to do: “If you come into contact with red tide, wash off with soap and water,” the Florida Department of Health advises.

Who is at increased risk for red tide-related illness?

Conditions: People with allergies, asthma and other respiratory conditions are more likely to have severe reactions to breathing red tide, which may cause a histamine response, according to health officials and doctors. Pople who suffer from chronic migraines and fatigue are more likely to suffer neurological symptoms from red tide exposure, the Roskamp Institute found.

Study: “We don’t have any detailed advice yet, but it’s probably very wise for them to try to avoid it. Folks that get migraine can end up in the ER,” Mullan said, citing a 2019 study published in “Harmful Algae” that found a correlation between ER visits for severe headache and red tide. People ages 55 and up were at increased risk, the study found.

How long do symptoms last?

Time frame: Red tide exposure symptoms usually go away within a few hours of leaving the affected area. If symptoms don’t clear up, health officials advise seeking medical attention.

Should you avoid the beach if there’s red tide?

Exposure: Health experts advise residents and visitors to use avoid exposure to red tide when possible — especially those with respiratory or neurological conditions that could make them more sensitive.

Recovery: While most people recover from symptoms quickly, experts warn that the potential long-term effects of the toxin are unknown.

Do masks or drugs help?

Limiting effects: Wearing a particle filter mask may limit the harmful effects of breathing red tide, health officials say.

Filter ratings: In a study published in 2021, University of Miami researchers found that masks with high filter performance ratings, such as N95 and R95 masks, are effective at filtering out toxins released by harmful algal blooms.

Over-the-counter drugs: Using over-the-counter antihistamines can also help decrease upper respiratory symptoms, the Florida Department of Health says.

AC: Indoors, air conditioning filters with high FPR or MERV ratings and HEPA filters can help reduce exposure to the toxins.

Will red tide affect your pet?

Dogs and cats: Like other mammals, dogs and cats are susceptible to the toxin released by red tide blooms.

Symptoms: “Red tide exposure can result in neurological and digestive symptoms that include tremors, seizures, stumbling, paralysis, vomiting, diarrhea and drooling,” the Northeast Animal Hospital in St. Petersburg says. “Your dog may also experience low heart rate and low blood pressure. Symptoms can develop within 30 minutes to one hour after exposure and must be treated quickly.”

What to do: Pet owners should contact a vet immediately if an animal shows symptoms after contact with water or fish affected by red tide.

Can you eat seafood during red tide?

Shellfish: Recreational harvest of shellfish is banned during red tide events. The shellfish can accumulate toxins that can make people sick when eaten.

In restaurants and stores: “Store-bought and restaurant-served shellfish are safe to eat during a bloom because the shellfish are monitored by the government for safety,” the Florida Fish and Wildlife Conservation Commission says. “Commercially available shellfish are often not locally harvested and, if harvested locally, are tested for red tide toxins before they are sold.”

Safe: Fish are also safe to eat if they are properly filleted with guts removed, FWC says. Fish that are found dead or distressed should not be eaten.

What questions remain about red tide health effects?

“Florida’s population has never been this large, so you now have many more people being exposed to these toxins,” Mullan said. “We’re in uncharted territory from a health perspective. So there’s some very basic medical questions about the toxin that we’re interested in finding out.”

At the Roskamp Institute, researchers next want to tackle the question of how much red tide toxin it takes to trigger neurological illness. The institute is seeking volunteers and funding for a study on individuals who have been heavily and repeatedly exposed to red tide.

Once the toxicity levels of red tide are better understood, it could help officials decide when to issue health warnings, Mullan said.

Other questions that still need to be answered, according to Mullan:

▪ What happens after repeated exposure? “Some people seem to become more sensitive.”

▪ How long does red tide stay in the body? “We know it gets into the bloodstream and it dissipates very quickly from the bloodstream. But it can take a lot longer to get out of the body. We don’t know where it goes. It’s very liquid soluble, and very soluble in fats. That’s one reason I think that once it gets into the body, it can hide in different fat stores.”

▪ What role does the immune system play in red tide response? “Do higher antibody levels offer more protection against it? Or is it the other way around, where the more your body is responding to it on the immune level, the more symptoms you get? We just don’t know.”

Red tide resources

Several online resources make it easy to check whether a particular county, beach or coastline in Southwest Florida are currently affected by a red tide bloom.

NOAA’s Red Tide Respiratory Forecast is updated several times a day with the level of red tide risk at specific beaches along the Gulf Coast, from Pinellas County through Collier County. Visit habforecast.gcoos.org.

Mote Marine Laboratory’s Beach Conditions Report is updated frequently by lifeguards and includes reports of red tide conditions, including respiratory irritation and dead fish, as well as other hazards on local beaches. Visit visitbeaches.org.

The Florida Fish and Wildlife Conservation Commission issues weekly red tide reports with conditions by county and maintains a map of red tide sampling around the state. Visit myfwc.com/research/redtide/statewide.

University of South Florida’s Red Tide Prediction and Tracking center provides short term forecasts of red tide’s movement around Tampa Bay and the west coast of Florida. Visit ocgweb.marine.usf.edu/hab_tracking.