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Seaweed Irritation

What Facts Should I Know about Seaweed Irritation?

Seaweed such as algae and coelenterates are found worldwide in salt water and fresh water and can cause skin irritation. Most algae and coelenterates cannot be seen by the naked eye, so exposures to them are usually accidental.

Can seaweed give you a rash?

Algae or coelenterates (for example, jellyfish) trapped underneath bathing suits usually cause a rash that results from irritation. Sometimes it is difficult to distinguish between seaweed and coelenterate-caused skin irritation. However, the seaweed rash usually occurs when swimmers have direct contact with Lyngbya majuscula seaweed when it gets under bathing suits or in areas where skin to skin contact occurs such as under the breasts or in the groin region. It is also common to see along the waistband of bathing suits. 

The seaweed occurs worldwide and resembles dark matted clumps of hair (gray, greenish-black, reddish and yellow colors) and produces two toxins that cause skin irritation.

Seaweed Irritation Symptoms

Itching, burning, redness are most common but in some people, blisters can develop. Swelling may occur in some individuals.

Seaweed Irritation Treatment

  • Scrub the irritated skin area with soap and water and flush it extensively with fresh water. Rinse with isopropyl alcohol (rubbing alcohol).
  • Hydrocortisone cream may be applied 2 to 3 times daily to relieve itching. Immediately discontinue if any signs of infection appear such as increased redness, drainage (pus), or fever.
  • Allergic reactions, such as itching or rash, should be treated in adults with diphenhydramine (Benadryl) 50 mg every 6 hours and ranitidine (Zantac) 150 mg tablet every 12 hours. Some patients may require oral steroids. Consult with a physician for treatment in children.
  • If the affected skin area shows any evidence of infection, such as redness with pus, pain, foul odor, increased warm to the area, or fever, then antibiotics are usually recommended. Patients should consult with a physician or health care professional for further evaluation if there are any signs of infection. Some antibiotics can cause an increased sensitivity to the sun, so use a sunscreen (at least SPF 15) and avoid direct sunlight if possible.

When to Seek Medical Care for Seaweed Irritation

Consult a doctor if any signs of infection or if any symptoms other than a local reaction (redness or itching) occurs on the skin.


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Reviewed on 2/1/2019
Medically reviewed by Michael E. Manning, MD; Board Certified Internal Medicine/Allergy & Immunology


Rademaker, Marius, Assoc. Prof. "Seaweed Dermatitis. DermNetNZ.org.

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