For centuries, the umbrella of edible jellyfish has been consumed in Asia, usually cooked and sliced in salads. Edible jellyfish has a type of collagen which acts as an auxiliary agent in preventing arthritis and some peptides with antihypertensive effect [1].

As well as the potential health benefits of jellyfish consumption, the United Nations Food and Agriculture Organization has recommended the use of jellyfish in food and cosmetics, in attempt to recover falling fish stocks [2]. Hence, a worldwide expansion of its consumption is expected.

Portugal has a native Rhizostomeae jellyfish, named Catostylus tagi by Haeckel in 1869, which occurs abundantly in the summer in the Sado and Tejo estuaries. Previous studies demonstrated that the umbrella of this species contains relevant concentrations of very long chain fatty acids, antioxidants, collagen, and taurine [3], making it a possible source of food supplements. However, jellyfish consumption is not common in Portugal although the country has one of the highest seafood consumption per capita in Europe (61.1 kg/capita) [4]. One of the reasons for this disinterest may be the well-known deleterious effects of jellyfish stings, such as acute cutaneous inflammation with erythema, swelling, vesicles, and bullae [5]. These reactions are attributed to the compounds stored in its nematocysts which are not present in the edible umbrella. Also, jellyfish occasionally induce cutaneous lesions through delayed allergic mechanisms [56] whereas immediate anaphylactic allergy to jellyfish stings is extremely rare, and there are only 2 case reports of anaphylaxis by jellyfish stings [78].

A recent study reports the first case of anaphylaxis, produced by the ingestion of salt-preserved jellyfish. Curiously, the patient was a surfer and was frequently stung by jellyfish [9].

As far as we know, the possibility of allergic reactions attributed to cross reactivity has not been ruled out yet, particularly in shellfish and fish allergic patients to whom small traces of the potential allergen may trigger severe reactions. Our aim is, therefore, to establish the safety of jellyfish ingestion in seafood allergic patients and, secondarily, if they liked it and were willing to introduce jellyfish in their diet.

Adult subjects (18–65 years) with evidence of IgE-mediated sensitization and severe systemic reactions to crustaceans, cephalopods and/or fish were selected. Participants were recruited from the food allergy unit of an Allergy Department of a University Hospital. A control group of atopic, nonfood allergic individuals were also invited to participate.

Twenty-five subjects were enrolled, including 20 patients with severe seafood allergy, most of them also had atopic comorbidities (Table 1) and 5 atopic, nonfood allergic, controls.

Skin prick-to-prick tests (SPPT) with raw and boiled umbrella were performed, as well as challenges with C. tagi umbrella in all subjects. The challenges were carried out on the same day. Four pastes were made with tiny round portions of cooked C. tagi mixed with normal mayonnaise at 5%, 10%, 15%, and 20% w/w, samples 1, 2, 3, and 4 respectively, with 15-minute intervals. The snack pastes were prepared a few minutes before consumption by spreading the paste on wheat toasts. Upon completion, subjects remained in observation and, in case of any delayed reaction, participants were instructed to contact the investigators. A 9-point hedonic scale was applied after sensory analysis and they were also asked to answer a short questionnaire.

The research ethics committee approved the study (Ethics Committee Centro Hospitalar São João / Faculty of Medicine, University of Porto - Ref. no CES 41-15, date of approval: 19 March 2015), and signed informed consent was obtained from all subjects.

All the participants had negative SPPT to raw or boiled C. tagi umbrella.

None of the 20 seafood severe allergic patients, nor the control subjects had immediate or late phase reactions to any of the pastes. No subjective symptoms were reported and therefore no medical intervention was necessary.

The participants rated the samples with a mean score of 6.75 ±0.91. Seventeen of the seafood allergic patients (85%) were willing to introduce C. tagi into their diet.

This study shows that C. tagi umbrella may be safely consumed by seafood allergic individuals. All the patients with severe crustacean, cephalopods and/or fish allergy, including 60% with anaphylaxis, tolerated all the pastes. Consequently, it is unlikely that individuals with a similar history of allergic reactions or milder reactions would react to this edible jellyfish and these findings could also be extrapolated to a larger nonallergic population.

To our knowledge, this is the first study evaluating the safety of an edible jellyfish in patients with severe seafood allergy, using skin tests and oral challenges.

These findings contribute to increase the data regarding jellyfish ingestion in seafood allergic patients. In spite of their food allergy and consequent food avoidance, the vast majority of patients appreciated C. tagi and were willing to include it in their diet.