Hot Tub Rash: Causes, Water Checks and When to See a Doctor

This page is general information, not medical advice. Only a doctor or other healthcare provider can tell what is causing a rash and whether it needs treatment. Use this page to check and fix the water.

Itchy skin after a soak has more than one possible cause. Some are about germs in the water, some are about irritation from the water chemistry, and some have nothing to do with the tub. The water part is what you can test and fix yourself.

What the CDC calls hot tub rash

According to the CDC, hot tub rash (also called Pseudomonas folliculitis) happens when contaminated water stays on the skin for a long time. The germ is common in water and soil. What the CDC describes:

an itchy, red, bumpy rash, sometimes with pus-filled blisters around hair follicles;
often worse under the swimsuit, where wet fabric held water against the skin;
usually showing up within a few days after using a poorly maintained hot tub.

The CDC says mild cases often clear up within a few days without treatment, and to check with a healthcare provider if the rash gets worse or happens more than once. Hot water uses up sanitizer faster than pool water does, which is one reason hot tubs are a common source.

Germs or irritation: what the pattern can tell you

These patterns are clues for checking the water, not a way to diagnose a rash. A rash that doesn't fit, or any rash that worries you, is a question for a doctor.

Rash patterns and what to check in the water (not a diagnosis)
What you notice	What it can point to in the water	What to check
Bumps around hair follicles, worst under the swimsuit, appearing a day or more after soaking; others who used the tub have it too	Germs in poorly kept water. This resembles the CDC's description of hot tub rash; only a healthcare provider can tell.	Sanitizer and pH right away; whether the tub was used with low or zero sanitizer; the filter
Dry, itchy, or red skin soon after a soak, on all skin that was in the water	Irritation from the water chemistry: chloramines (used-up chlorine), very high sanitizer, or pH out of range	Free chlorine (FC) and total chlorine (to find combined chlorine), bromine level, pH
The same person reacts every time in a bromine tub, others don't	A possible reaction to bromine; skin reactions have been reported in research. Only a doctor can tell.	Bromine level; talk to a doctor; compare other sanitizers
Rash only after a new product, or after a shock	Soaking before the level dropped back, or a product your skin reacts to	Whether the label's waiting time and swim limit were followed

Check the water

Test right away, before you add anything, so you know what the water was like. The CDC's ranges for hot tubs:

Hot tub water checks (CDC)
Test	CDC range	If it's off
Free chlorine (FC), chlorine tubs	At least 3 ppm; the CDC says to tell the owner or operator if it is above 10 ppm	Low: add chlorine (hot tub chlorine calculator). Above your label's limit: no soaking until it drops.
Bromine, bromine tubs	4–8 ppm	Adjust the feeder or dose (hot tub bromine)
pH	7.0–7.8	Correct it (pH too high, pH too low)
Combined chlorine (total chlorine − FC)	Not in the CDC list; we flag 0.5 ppm or more	Shock per your product's label (hot tub shock)
Water temperature	No higher than 104 °F	Turn it down (hot tub temperature)

The calculator below is set for a hot tub without stabilizer. It shows a free chlorine minimum of 3 ppm, in line with the CDC, and a target of 3–5 ppm. Enter your reading to see where you stand.

Strips are fine for a first check; the CDC recommends a DPD test kit for more accurate readings. If your tub has stabilizer (CYA) from long use of dichlor (stabilized chlorine granules), the free chlorine reading can look fine while the chlorine works more slowly. The CDC recommends not using CYA in hot tubs. The hot tub chemical calculator checks all your readings at once.

Bromine and skin irritation

Bromine is a common hot tub sanitizer, and most people use it without trouble. A 2017 review of bromine in pool water reported several cases of irritant skin reactions linked to bromine tablets (BCDMH) in hot tubs. The same review notes that Pseudomonas aeruginosa, the germ behind hot tub rash, is more resistant to bromine than some other bacteria, so letting bromine drop below range is not the answer either.

If one person reacts every time, keep bromine within 4–8 ppm, rinse off after soaking, and talk to a doctor. Some owners switch sanitizers; the trade-offs are on hot tub sanitizers compared.

Fixing the water after a rash

If the water was low on sanitizer, or you can't tell how long it was low, the simplest reset is a full clean:

Keep everyone out of the tub.
Flush the plumbing with a hot tub line cleaner, following its label, then drain the tub. Germs that cause hot tub rash can hide in biofilm (a slimy layer) inside pipes and jets. See how to flush hot tub lines.
Scrub the shell, jets, headrests, and the underside of the cover. Clean or replace the filter.
Refill, balance pH, and bring sanitizer into the CDC range. The first-fill steps walk through it.
Test before each use for the next few weeks, and keep the levels in range between soaks.

If the water tested in range, still clean the filter and check that the circulation and the ozone or UV unit, if you have one, are working. Then look at the other patterns in the table above with your doctor.

Prevent it next time

Shower before you get in (CDC).
After soaking, take off your swimsuit and shower with soap, and wash the swimsuit (CDC).
Test sanitizer and pH before each use in a busy week, and at least a few times a week otherwise.
Don't let sanitizer hit zero between uses. A tub that sits warm with no sanitizer is the classic setup for hot tub rash.
Change the water on schedule; the water change calculator estimates how often for your tub and use.

Health and safety. Pooldex does not give medical advice. See a doctor or other healthcare provider about any rash that gets worse, doesn't go away, or keeps coming back. Always follow your product labels, including the level and waiting time before soaking. It is a violation of federal law to use a pesticide product in a manner inconsistent with its labeling. Never mix chemicals. In an emergency, such as trouble breathing after chemical exposure or chemicals in the eyes, call 911 or Poison Control at 1-800-222-1222.

FAQ

How long does hot tub rash last?

The CDC says mild cases often clear up within a few days without medical treatment. If the rash gets worse, lasts, or comes back, check with a healthcare provider.

Can bromine cause a rash?

It can in some people. A research review reported cases of skin irritation linked to bromine tablets in hot tubs. If one person reacts each time while others don't, keep bromine in the 4–8 ppm range and talk to a doctor.

Should I drain the hot tub after someone gets a rash?

If the sanitizer was low or you don't know how long it was low, yes: flush the lines, drain, scrub, clean the filter, and refill. It is the quickest way to start from clean water.

Can you get hot tub rash from a tub with good chlorine levels?

It is much less likely when sanitizer and pH stay in the CDC ranges, but levels can drop between tests, especially with heavy use and hot water. Test before soaking, and shower and change out of your swimsuit afterward.

Sources

CDC, Preventing hot tub rash (cause, symptoms, timing, when to see a healthcare provider, prevention, water levels): cdc.gov
CDC, What you can do to stay healthy in hot tubs (chlorine, bromine, pH, 104 °F): cdc.gov
CDC, Home pool and hot tub water treatment and testing (DPD kits; no CYA in hot tubs): cdc.gov
CDC, MMWR 2000, Pseudomonas dermatitis/folliculitis associated with pools and hot tubs, Colorado and Maine, 1999–2000 (higher temperatures dissipate chlorine rapidly): cdc.gov
CDC, Controlling Legionella in hot tubs (biofilm in hot tub plumbing): cdc.gov
Lagiere J. and others, Bromine chemistry applied to disinfection of swimming pool water: a literature review, Revue des sciences de l'eau, 2017: erudit.org