Seaweed Allergies: Skin Irritation and Food Sensitivity

Seaweed is another name for macroalgae, which are multicellular marine organisms that are photosynthetic, meaning they derive their energy from sunlight. Seaweed is present globally in every climate, but more commonly causes problems in locations such as the Pacific Ocean, which include allergies and skin irritation.

Key takeaways:
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    Stinging seaweed disease occurs frequently in some locations such as Hawaii and the locals call it “stinging limu”.
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    Often, the seaweed itself does not cause skin irritation. Rather it is the algae and/or jellyfish entwined with the seaweed.
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    Avoiding clumps of seaweed or staying out of the ocean may be the best prevention.
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    Treatment is supportive, including antihistamines, steroids, or antibiotics in severe cases.
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    Seaweed has been recognized as a source of food allergy, particularly the Nori seaweed. Identification and avoidance are the best treatments.

Seaweed is not plants, animals, or fungi, but instead is known as protists. It represents a critical link in the marine food chain.

Seaweed is classified based on its pigmentation: red (Rhodophyta), brown (Phaeophyceae), and green (Chlorophyta). Edible seaweed is popular in East Asia in countries such as Japan, China, and Korea. Some seaweed is used as food wrapping or consumed as sea vegetables. Recently, it has been recognized that it is possible to have a food allergy to seaweed if ingested.

It is more common to have skin irritation or a rash due to direct contact with seaweed in both salt and freshwater. This article reviews the signs and symptoms and treatment of both skin irritation (“stinging seaweed disease”) and food allergy by consuming seaweed.

What is stinging seaweed disease?

Skin irritation that goes along with direct exposure to seaweed may be caused by contact with toxin-producing algae called Lyngbya majuscula or jellyfish exposure. Often the algae or jellyfish cannot be seen even though the seaweed can.

Lyngbya majuscula causes contact dermatitis. It is a blue-green alga that can survive up to 100 feet deep. Many people call the seaweed and algae clumps “mermaid hair” or “fireweed.”

In places such as Hawaii for example, algae and jellyfish can get caught in your bathing suit along with seaweed. It may be common to have stinging where you don’t expect or want, such as under the arms, under the breasts, in the groin area, or along the waistband. Hawaiians call stinging seaweed “stinging limu.”

It is often impossible to tell what exactly caused the skin irritation. It could be the seaweed itself or either the algae or jellyfish or all of the above. It may be impossible to avoid stinging seaweed disease in some cases where there are strong currents and wind.

In most locales, the risk of exposure occurs only at certain times of the year.

The only sure way to avoid stinging seaweed disease is to stay out of the water, particularly if there are reports of stinging seaweed in the area. If you think you have been exposed, make sure you shower or bathe with copious amounts of soap and water and wash all of your swimsuits, towels, or any other clothing that may have been exposed as well.

What are the signs and symptoms of stinging seaweed disease?

Most people develop a skin rash and/or blisters (especially in the genital and anal areas) but there can be other signs and symptoms such as:

  • Itching and burning.
  • Swollen eyes.
  • Skin sores.
  • Oral and intestinal irritation.
  • Headache.
  • Fatigue.
  • Fever.

Typically, the symptoms and rash last from several minutes to several hours. However, the skin sores can linger for more than a week in severe cases.

How is stinging seaweed disease treated?

In addition to cleansing with soap and water, isopropyl alcohol helps. Hydrocortisone cream is very helpful to reduce the inflammation and redness of the skin. Make sure you stop the hydrocortisone if there is pus-like drainage from the skin sores or a fever develops. That may indicate that you need to seek medical treatment.

Allergic reactions are fairly common. Treatment should include:

  • Diphenhydramine (Benadryl) or chlorpheniramine antihistamine.
  • A heartburn medicine such as esomeprazole (Nexium) or lansoprazole (Prevacid), or another equivalent. These also have antihistamine characteristics.
  • Oral steroids, in some cases.
  • Antibiotics may be necessary if the skin sores show signs of infection such as foul odor, pus, pain, increased warmth, and fever.

What about swimmer’s itch? Is it the same thing?

There are other causes of dermatitis when swimming. The other most common one is called “swimmer’s itch” or cercarial dermatitis. It causes a skin rash as a result of an allergy to microscopic parasites. It is treated similarly except it may require cool compresses, Epsom salts, baking soda, and colloidal oatmeal baths as well.

The skin rash usually occurs everywhere the body is not covered. Therefore, it is opposite to the rash from seaweed and does not affect the genital areas.

Can you be allergic to eating seaweed?

Yes, the first published report of an allergy to consuming seaweed was published in 2018. The report referred to an allergy to red (Nori) seaweed. It was noted that if someone is allergic to consuming one type of seaweed, it is likely that a person may still be able to tolerate eating other types of seaweed. The person would need to risk trying another type of seaweed or conduct a food challenge.

East Asian cultures, particularly in Japan, have used seaweed in their meals for centuries. Now, with the focus on sustainability, there is increased interest in consuming alternative protein sources other than animals.

However, there may be risks. There are potential hazards to using seaweed in food such as exposure to toxins, pesticides, pathogens, biotoxins, and allergies.

It is thought that eating Nori or dried seaweed is healthy. It can offer nutrients, minerals (calcium and iron), vitamins A and C, and dietary fiber.

The concern is that Nori is often contaminated with other potential allergens such as shellfish, fish, or particularly a crustacean species (amphipods) or shrimp. The allergy that people experience when eating Nori can be more related to the ingestion of the shrimp, which contaminates the seaweed. There is limited research on this potential allergic hazard.

Treatment of food allergy may be challenging depending on the severity of the person’s reaction. The allergy treatment may require antihistamines, steroids, or even airway management if there are severe respiratory symptoms. Identification of the potential allergy may be key in preventing the allergic reaction and for some individuals that may be trial and error, unfortunately.

Yes, it’s possible to be allergic to seaweed, both through contact with your skin and if you eat it, especially the Nori form used in Japanese cuisine. Treatment ranges from topical to drugs such as steroids and antibiotics for the skin rash, along with antihistamines or airway management in severe cases of respiratory distress when a person eats seaweed.


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