What might cause this rash on the beach?

[TheHorneSection]

12yo DD has come out in hives after being in the sea and on the beach. We used our usual sunscreen so I don’t think it’s that, it was cloudy and muggy so it’s not sunburn, and wouldn’t have said it was windy enough for windburn but you never know. Showed it to a pharmacist who wasn’t worried and just gave us antihistamines and some itch cream (she feels absolutely fine bar the skin being a bit tender). Any ideas what might have caused it, so we can try and avoid it again? We’re in the UK if that makes a difference, Norfolk coast.

There are some seaweeds that sting. Could it be that?

DH was stung by seaweed once. It was sore for a couple of hours but fine after a shower and an antihistamine.

Most likely swimmer’s itch (cercarial dermatitis)

You can still get sunburn even if it's cloudy....

Heat rash. Doesn't even have to be that warm. My skin reacts to UV light and I get a rash like that. Unbearably itchy but sore to touch.

Piriton and Eurax cream.

My heat rash looks identical to that. Although usually on more areas.

I don't get it anymore for some reason.

Thanks, we’ll treat it like heat rash - it’s funny as it’s normally me who reacts and she never does but there you go! Have piriton and Eurax and will force her in a cold shower later with some after sun after.

Everywhere on my body that had been in the water went like that, and afterwards I found out the water wasn’t terribly clean that day (I’ve swapped to a different beach)

Antihistamines sorted me out, and a thorough rinse in cool water

my 8 year old got this last year from a day of sun and pool swimming (not that hot and it def wasnt' sunburn as they were wearing a rashshirt) normally it's me but I was fine. One antihistamine cured it and it's never come back, despite much swimming and sun.