Sea lice bites or jellyfish stings?
During spring and summer, Auckland Regional Public Health Service (ARPHS) often receives reports of swimmers suffering rashes after swimming at Auckland’s beaches, particularly those bordering the Hauraki Gulf.
These itchy, sore rashes are often assumed to be due to sea lice bites, but it is more likely that they are caused by contact with microscopic jellyfish. The resulting rashes are known as ‘Sea Bather’s Eruption’.
What is Sea Bathers Eruption?
Sea Bather’s Eruption is an itchy or painful rash which tends to affect the areas of the skin covered by swimwear, rather than exposed areas, after swimming in the sea. It is the skin’s reaction to the toxin injected by jellyfish stinging cells, which tends to occur after the person has left the water. Children are most affected - probably due to their softer skin. Those prone to allergic skin reactions are also more likely to be severely affected.
How does Sea Bathers Eruption occur?
Warm weather and onshore winds bring the tiny organisms close to the shoreline. Being microscopic and largely transparent, they become trapped unnoticed in swimwear, or in peoples’ hair. As the swimmer gets out of the sea, water drains from the swimwear and traps the organisms between the fabric and the skin, causing the stinging cells to release their toxin. Each organism has several of these stinging cells. Unfortunately, most of the things swimmers typically do after a dip make the situation worse; wearing swimwear for prolonged periods, drying with a towel, and the osmotic changes in jellyfish that result from rinsing off with freshwater can all increase the chances of the jellyfish discharging toxin. Note that if someone has suffered from Sea Bather’s Eruption, their swimming costume should be washed and rinsed thoroughly to remove the organisms, as cells that have dried out can still sting on contact, even several weeks later.
What does Sea Bather’s Eruption look like?
The typical rash of Sea Bather’s eruption is shown in the photo below.
The uncomfortable rash caused by Sea Bather's Eruption is most pronounced in areas where a person’s swimwear clings to the skin.
What are the health risks to humans from Sea Bather’s Eruption?
Generally, those affected have an itchy red rash on areas that were covered by swimwear. The rash can vary from mild to severe. It can last for a week or more.
How can I treat Sea Bather’s Eruption?
Calamine lotion, antihistamines and mild steroid creams like 0.5% or 1% hydrocortisone may be helpful, and can be bought from a pharmacy. Your local pharmacist should be able to advise you. Some children become unwell with headaches, nausea and lethargy for several days.
How do we know it isn’t just sea lice?
Sea lice are fish parasites, and do not bite humans. Sea Bather’s Eruption occurs mainly under swimwear, and can be made up of hundreds to thousands of little red dots that can join together, making larger patches, or appear as weals.
What can be done to avoid getting stung?
The only certain way to prevent being stung during risk periods (generally the warmer months) is to avoid sea bathing at affected beaches.
During the summer, all beaches in the Hauraki Gulf can be affected. This includes all the popular North Shore and Eastern Bays beaches. Below is a list of things you can do to reduce the risk if you choose to swim in the ocean:
- Do not wear large, baggy clothes into the water. Smaller bathing costumes are better, because they trap fewer jellyfish. ‘Speedo-style’ swimwear and bikinis are best, but remember to wear plenty of sunscreen, especially on areas of paler skin.
- After swimming, remove your swimwear as soon as possible and then shower if you can – especially the area that was covered by your swim wear. If there is a saltwater shower, it is best to use that. If not, a freshwater shower is almost as good. Consider changing into a second pair of togs for public showers on beaches.
- Don’t towel off before showering – this will just set off the stinging.
- Don’t sit around on the beach in the swimwear you swam in – change into another costume, or other clothing.
- Don’t wear the swimwear again until it has been washed and rinsed thoroughly, as the jellyfish can still sting even after they are dead. It is possible to get stung weeks after initial contact if the swimwear has not been thoroughly laundered.
Found New Zealand-wide, the bluebottle jellyfish (Physalia utriculus) is the species that most commonly causes stings. The lion’s mane jellyfish (Cyanea capillata) can also wash up on our beaches in large numbers. These stings are generally mild. Other jellyfish may sting, but are unlikely to cause major health effects.
If a swimmer wears a mask or swimming goggles, they are much more likely to see the larger jellyfish underwater in time to avoid them. A wetsuit will provide protection from these large jellyfish in the areas covered. Gloves and boots would protect hands and feet but the face will always be partly uncovered, even when wearing a mask.
What are the symptoms of jellyfish stings?
Most jellyfish stings in New Zealand are not serious and, if given prompt first aid, people are not likely to develop significant symptoms. Symptoms of jellyfish stings include immediate intense pain, with burning and itching at the site of the sting. The sting often appears as a weal with surrounding redness. Rarely, victims can develop symptoms such as breathing difficulty or loss of consciousness.
How do I treat a jellyfish sting?
- Wash the affected area with fresh or saltwater.
- Remove any tentacles or stings attached to the skin – but do not touch the tentacles or stings with your bare hands.
- Place the affected area in warm water (45C).
- Do not apply vinegar, methylated spirits or alcohol, as these will make the sting more painful.
If the reaction to the sting is severe or the symptoms worsen, calamine lotion, antihistamines and steroid creams may be helpful. Your local pharmacist should be able to advise you. If the person develops reduced consciousness or difficulty breathing call 111 and ask for an ambulance.
Please phone ARPHS on 09 623 4600 and ask for the duty Health Protection Officer in the Environmental Health team if you require further advice on this matter.