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Hot Tub Rash: Itchy Red Bumps After Your Hot Tub — Causes & How to Fix It

Got an itchy, red, bumpy rash a day or two after a hot tub session — worse where your swimsuit sat against your skin? That's almost certainly hot tub rash, properly called Pseudomonas folliculitis. It's harmless in most cases and usually clears on its own, but it's a clear warning sign: the bacteria that caused it are living in your hot tub, and they'll keep doing it until you clean the tub properly.

This guide covers what the rash is, how to treat your skin, and — the part that actually matters — how to clear the bacteria and biofilm out of the tub so it doesn't keep happening.

What Hot Tub Rash Looks Like

Hot tub rash typically appears a few hours to five days after you've been in a poorly maintained tub. Tell-tale signs:

• Itchy, red, bumpy rash centred on the hair follicles
• Pus-filled blisters or spots around the follicles — it can look a bit like acne
• Worse under swimwear — the buttocks, hips and torso are most affected, because a wet swimsuit held the contaminated water against the skin for longest
• Sometimes a burning or stinging feeling rather than just itch
• In some people, feeling generally unwell — mild fever, headache, sore throat, swollen tender glands, earache

A classic giveaway: several people who shared the same hot tub all break out at once a day or two later. That's because they all picked it up from the same contaminated water — the rash itself isn't really passed person to person.

What Causes It

The culprit is Pseudomonas aeruginosa, a common bacterium found in water and soil. It loves warm, wet environments — which makes a hot tub close to ideal. It infects the hair follicles, which is why the rash is bumpy and follicle-centred.

Here's the important bit: Pseudomonas can survive in a hot tub even when the water looks perfectly clean and is chlorinated. It does this by forming a biofilm — a slimy protective layer on the tub surfaces and, crucially, deep inside the pipework, jets, air channels and filter, where your sanitiser struggles to reach. Organic material left behind by bathers (skin, oils, sweat) feeds it.

So the bacteria sit safe inside the biofilm, periodically shedding back into the water. Your test strips might even look fine. But the moment free chlorine dips — after a busy soak, or if the tub's been sitting warm and under-sanitised — the bacteria multiply and the next person out gets the rash.

Treating the Rash (Your Skin)

The good news is that hot tub rash is usually mild and self-limiting. Most cases clear up on their own within a few days to two weeks without any specific treatment.

• Anti-itch relief — an over-the-counter hydrocortisone cream or anti-itch lotion eases the itching and inflammation.
• Keep the area clean and dry, and avoid scratching to prevent secondary infection.
• Don't go back in the tub until it's been cleaned — re-exposure restarts the whole thing.

This is general information, not medical advice — if you're worried about a rash, speak to a pharmacist, NHS 111 or your GP.

Fixing the Tub (The Part That Stops It Coming Back)

Treating your skin clears the symptom. Cleaning the tub clears the cause. Because the bacteria hide in biofilm, simply shocking the open water isn't enough — you have to get into the plumbing.

1. Stop using the tub until it's done. Every soak before then re-seeds your skin.
2. Test and balance — use 6-in-1 strips. Bring pH to 7.2-7.6 first; chlorine is far more effective in range (at pH 7.2 most chlorine is the active killing form; at pH 8 most of it is inert).
3. Shock the water — chlorine granules at the shock rate (~20g per 1000 litres), pre-dissolved in warm water, pump running, cover off for the first hour. Kills bacteria in the open water.
4. Flush the plumbing — add a spa pipe-purge / system-flush product, run all jets and the air blower for 20-30 minutes so it scours the biofilm out of the internal pipework, then drain it away. This is the step that actually removes the Pseudomonas reservoir.
5. Deep-clean the filter — soak the cartridge in cartridge cleaner overnight; replace it if it's over 12 months old or visibly clogged. A dirty filter is a biofilm farm.
6. Wipe the shell, scum line and cover underside — biofilm and mould collect there too.
7. Drain, refill and re-sanitise — fresh water, re-balance, bring free chlorine to 3-5mg/L. Only get back in once the water's balanced and your skin has cleared.

Safe Water Levels: Quick Reference

Prevention: Stopping the Rash Coming Back

When It Keeps Happening — Get the Tub Checked

If you've shocked, flushed, replaced the filter and drained and refilled, but people keep getting the rash, the biofilm may be entrenched in dead-leg pipework — sections where water barely circulates and sanitiser and flush can't reach. Weak circulation makes this far worse, because the whole system never gets properly cleaned.

• Weak circulation / flow faults — see our E02 flow-error guide.
• Recurring smells alongside the rash — musty or eggy smells point to the same biofilm; see hot tub water smells.
• Cloudy or foamy water — often the same bacterial/organic load in visible form; see cloudy & foamy water.

Products You'll Need

All available at B&Q Bournemouth, Amazon, or directly from Lay-Z-Spa.co.uk:

• 6-in-1 test strips — chlorine, bromine, pH, alkalinity, hardness (~£8 for 50)
• Chlorine granules — for dosing and shock (~£8-12 for 1kg)
• Spa pipe-flush / system purge — strips biofilm from internal plumbing (~£8-12)
• Filter cartridge cleaner — overnight soak (~£6-9)
• pH Plus / pH Minus — to balance the water (~£6-8 each)
• Hydrocortisone cream — over-the-counter, eases the itch on your skin (~£4-6)
• Hose pre-filter — reduces minerals on refill (~£20, reusable)

Frequently Asked Questions