In this trial, we tested the effectiveness of jellyfish sting inhibitor cream compared with conventional sunscreen lotion and no prophylaxis before exposure to jellyfish tentacles. We found that the use of jellyfish sting inhibitor reduced the number of subjects who suffered discomfort, and the number of objective findings. The discomfort was also less severe.
These results are consistent with the few published studies of the use of jellyfish sting inhibitor cream, although the studies have somewhat different methodology and other types of jellyfish were used. In a field trial from the Gulf of Mexico the protection provided by jellyfish sting inhibitor lotion (Safe Sea) compared with conventional sunscreen was tested on ten voluntary snorkellers (1). One of the two lotions was applied to the right and one to the left half of the body. The subjects snorkelled a total of 82 times in seawater for around 30 minutes. Two symptom-generating contacts with jellyfish were registered on the skin areas that had received jellyfish protection, compared with 11 on the areas to which conventional sunscreen had been applied (p = 0.02). In another trial with a method more like our trial, 23 subjects were tested with inhibitor lotion (Safe Sea) or conventional sunscreen lotion (Coppertone) on the forearm (8). All of the 12 trial subjects who were exposed to the jellyfish Chrysaora fuscescens developed erythema and experienced pain on the areas of the skin to which conventional sunscreen had been applied, while erythema was found and pain registered only in two trial subjects whose skin had been creamed with jellyfish sting inhibitor (p < 0.01). Twelve subjects were tested against the box jellyfish Chiropsalmus quadrumanus, and erythema and pain were registered in ten and nine, respectively, of these who had received conventional sunscreen, compared with one and three of those who had received jellyfish sting inhibitor (p < 0.01).
The advantage of our trial compared with previous studies is a higher number of trial subjects and that the jellyfish sting inhibitor cream was also tested against no prophylaxis. We also made greater efforts in the trial to measure the time before pain/discomfort occurred and to compare the effect of the jellyfish sting inhibitor cream with conventional sunscreen or no cream. The jellyfish that are most prevalent in Norwegian seawater were used. We therefore believe that this trial is appropriate for Northern European conditions.
The weakness of our model is that we investigated the effect of three different treatments, of which each subject only received two. However, we have taken this into account in our statistical analyses. The reason for our comparison of the jellyfish sting inhibitor cream with both conventional sunscreen and no treatment was that electron microscope studies have shown that conventional water-repellent sunscreen can have a protective effect against cnidocytes compared with no prophylaxis (11). We found greater differences between the jellyfish inhibitor lotion and no prophylaxis than between the inhibitor lotion and conventional sunscreen, but no statistically significant difference between conventional sunscreen and no prophylaxis. It is possible that by increasing the number of trial subjects we could have demonstrated such a difference, but it is uncertain whether it would have had any clinically significant relevance. It ought also to be noted that we had no negative control, and that the trial was only blinded with respect to prophylaxis with jellyfish inhibitor and conventional sunscreen. This blinding was not possible for subjects who received no prophylaxis, which could influence the registrations of the trial subjects.
As most sea-bathers have experienced, pain/discomfort commences virtually immediately after exposure to jellyfish tentacles, corresponding to the time when the cnidocytes fire the toxins into the skin. This normally occurs at the first touch. In our trial, we registered pain/discomfort at different times in the course of the four minutes the subjects were exposed to tentacles, even though many of those who did not receive prophylaxis registered pain/discomfort within 150 seconds. This may be because we tested the subjects with a relatively small quantity of jellyfish tentacles in a relatively small area. Some of the cnidocytes had also already been activated while being moved from the sea to the trial premises and thus were no longer potentially harmful. We chose a relatively long exposure time in order to be sure that some of the cnidocytes were activated against the trial subjects’ skin and thus could provoke pain/discomfort. We did not investigate the effect of an exposure time longer than four minutes, but we believe this time is satisfactory viewed in relation to expected exposure time in ordinary seawater. None of those who did not experience pain/discomfort during exposure developed pain/discomfort after the tentacles had been removed. This may indicate that the risk of developing symptoms in the time after exposure is limited.
The jellyfish sting inhibitor effect may be attributed to a number of factors (1). The cream is very hydrophobic, and therefore reduces the number of tentacles that come into contact with the skin. The cream contains glycosaminoglycans similar to those in the jellyfish, and receptor antagonists that trigger the cnidocyte receptors on activation. The cream also contains substances that block calcium and magnesium exchange in the cnidocytes’ cnidocysts and therefore reduce the osmotic pressure for transferring cnidocyte toxin. Although this can reduce the quantity of toxins a subject is exposed to, the cream will not neutralise the effect of any toxin that enters the skin.
The treatment strategy described earlier in Tidsskriftet (5, 6) therefore remains relevant for those persons who develop topical or systemic symptoms. After exposure, tentacles should be removed carefully with tweezers and/or rinsed off with seawater. A medium for deactivating cnidocytes should not be used unless one is sure of the mechanism by which the medium affects that specific jellyfish. At worst it could exacerbate the situation, for example the use of vinegar against the lion’s mane jellyfish. After all tentacles have been removed, topical reactions can be dampened with lidocaine gel or corticosteroid cream. Peroral medicines such as paracetamol, non-steroid anti-inflammatories, antihistamines and steroids may also be considered. In the case of systemic reactions the patient should be observed or hospitalised.