Seaweeds are aquatic plants or algae, there are thousands of species and they are loosely defined by their colour, red, brown or green. They are used in farming as food for cattle or fertiliser and have been used as human food for thousands of years.

Carrageenan are made from red seaweed and are used in foods as thickeners and stabilisers. The E-number for carrageenan is E407.

Agar is also made from certain species of red seaweed. It is a jelly-like substance which is used in medicine (agar plates) and as a plant based gelatin replacement. The E-number for agar is E406.

Alginates are made from certain brown seaweeds. They are efficient at absorbing water, so are used in dietary supplements and gaviscon as well as being used in fireproofing materials.

Specific allergens are difficult to study as seaweeds are from such a diverse group of plants. A Chitinase protein has been found in Porphyra yezoensis, a red seaweed used to make nori. Another species of Porphyra, Porphyra umbilicalis, is also a red seaweed used to make Laverbread.

Seaweeds are generally low histamine, but nori is high in other biogenic amines similar to histamine, so is not suitable for people following a low histamine diet.

Seaweed is a low FODMAP food. FODMAP stands for Fermentable oligosaccharides, disaccharides, monosaccharides and polyols. Foods high in FODMAPs can cause symptoms of food intolerance, affecting the gastro intestinal system and this can be mistaken for a true IgE food allergy.

Seaweed, more specifically nori, is a food high in salicylates. Salicylates have the potential to cause worsening of asthma, swelling, itching and hives as well as food intolerance symptoms in people who are sensitive to salicylates.

You can read more about Food Intolerances on the dedicated Food Intolerance Page.

Seaweed dermatitis is caused by contact with certain species of seaweed, usually when wading or swimming in the sea. The most common cause of this is the seaweed, Lyngbya. It releases toxins which can be rubbed into the skin if the plant is caught in a damp swimming costume.

Other foods which contain chitinases include avocado, banana, cashews, coffee, corn, grapes, kiwi, passion fruit and pomegranate.

Note these food lists are not exhaustive, you can find the most up to date information on the Cross Reactivity Tool.

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