Microscopic jellyfish could be the real culprit for the painful rash developed by some Western Bay beach-goers.
A Tauranga pharmacist put the rash down to bites from a bug dubbed the "Mount Mauler", but a bug expert suggested it was more likely to be sandflies.
In a new twist, a former public health service staff member yesterday told the Bay of Plenty Times she believed the real culprits were microscopic jellyfish called hydromedusae.
Her son came home covered in small lumps after swimming at Waihi Beach at the weekend and she recognised it from her days in the health industry.
The woman, who refused to be named, said she had been stung by the creatures while swimming on Auckland's East Coast many years ago.
"It's terrible. Really really bad. It lasts for a long time, at least a week. As soon as I saw it on my son I knew."
A fact sheet produced by the Auckland Regional Public Health Service said the rash caused by the jellyfish was known as "sea bather's eruption" and had been a common problem at Auckland beaches in recent years.
"Warm weather and onshore winds bring the tiny organisms close to the shoreline. Being microscopic and largely transparent they become trapped underneath swim wear or in peoples' hair. Generally, as the swimmer gets out of the sea, water drains from the swim wear and traps the organisms between the fabric and the skin, causing the stinging cells to release toxin into the skin."
The fact sheet warned swimmers against wearing swim wear for long periods after swimming as the organisms often became trapped and continued to sting. Rubbing them with a towel while drying and freshwater could also cause them to discharge the toxin.
Calamine lotion, mild steroid creams and antihistamine tablets could reduce the discomfort.
Toi Te Ora Public Health Service medical officer of health Dr Jim Miller said he had received no reports of bites or stings during the summer.
If such jellyfish were causing rashes the treatment suggested by the Auckland Regional Public Health Service would be the best course of action, he said.
Neither Tauranga City Council or the Bay of Plenty Regional Council had reports of hydromedusae in the area.