Most hot tub worries are about heat. The rash is a water problem, and CDC names both its cause and the steps that prevent it.
This article covers what the Centers for Disease Control and Prevention says about it. It sits under our overview of hot tub benefits. It is general information, not medical advice.
Short answer: hot tub rash is a rash around the hair follicles, caused by the germ Pseudomonas aeruginosa. It usually shows up a few days after sitting in a poorly maintained tub, and it’s often worst under a swimsuit. CDC’s prevention advice comes down to keeping disinfectant and pH in range, then showering and washing your swimsuit after you soak.
What it is
CDC calls it Pseudomonas folliculitis. The germ is common in the environment, in water and soil, and the rash can develop when contaminated water stays on the skin for a long time.
What it looks like and when
CDC describes:
- Itchy, red, bumpy skin
- Sometimes pus-filled blisters around hair follicles
- Onset usually a few days after sitting in a poorly maintained hot tub
Anyone can get it, at any age. CDC says it’s often worse where a swimsuit held contaminated water against the skin.
The water levels CDC recommends
Here’s what the spec sheet won’t tell you: CDC’s advice rests on disinfectant and pH levels, and the only way to know them is to test.
| Measure | CDC level |
|---|---|
| Free chlorine | At least 3 ppm; above 10 ppm, CDC says to contact the operator or owner |
| Bromine | 4 to 8 ppm |
| pH | 7.0 to 7.8 |
CDC’s home hot tub page says to test chlorine and pH at least twice a day, more often when many people use the tub. It adds that hot tub jets create droplets or mists that can reduce chlorine levels. It also recommends not using cyanuric acid, or chlorine products that contain it such as dichlor or trichlor, in hot tubs.
Test strips make the checks quick. The AquaChek 7-way strips read free chlorine, bromine, and pH, among others, from one dip. Amazon sets the price. Reading Water Test Strips explains each pad.
CDC’s prevention steps
- Take off your swimsuit and shower with soap after you get out.
- Wash your swimsuit after each use.
- Check disinfectant and pH with test strips.
If you’re using someone else’s tub and the levels are out of range, CDC says to tell the operator or owner right away.
When to see a provider
CDC says mild rashes usually clear within a few days without treatment. Check with a healthcare provider if the rash gets worse or if you get it more than once.
My rule of thumb for owners: the rash is a sign the water care slipped. Test before you look for any other cause.
Bottom line: hot tub rash comes from water that wasn’t kept disinfected. Hold chlorine or bromine and pH in CDC’s ranges, test often, and shower after you soak. For the bigger picture on soaking and health, see the hot tub benefits overview linked above.