Persulfates are primarily used as shock treatments for pools and hot tubs.  This is different than the chlorine or other treatments that are used to prevent algae growth.  Most people who have problems from persulfates get the problem from a hot tub.  Less common exposure is through hair bleaching products.

Other names include:

•  Peroxymonosulfate
• Peroxydisulfate
•  Peroxydisulphate
• Monopersulfate    

What kind of rash does it cause?

Most people who are allergic to MPS will get a severe rash over their legs, trunk, and arms.  It usually affects either the calves or the inner, upper arms particularly severely, although it can affect anywhere that comes into contact with the water.

Almost all shock treatments use potassium peroxymonosulfate (PPMS) or related chemicals.  Even though the shock treatment may only be added once every few weeks, if it has been added to the water at any time, then getting in the water for a few minutes will usually make the rash flare up, usually starting that night or the next day.  

The rash and itching will start to get better if you avoid persulfates completely for 1-2 weeks.  Most people notice a big difference after about a month of avoidance, and it usually takes 3-6 months to get completely better. 

How to avoid it:

If you have a hot tub and want to continue using it, you must drain it and refill it with fresh water.  Be very careful to never add any chemical that has a persulfate in it.  Instead of a persulfate based shock, you can either use hyperchlorination, hydrogen peroxide, bromine based chemicals or you can drain the water every few weeks and refill it.  Talk to your spa dealer about these options.

You should also avoid hot tubs in hotels or at other people’s houses, as these most likely are shocked using MPS.  Pools are usually OK, but some public pools may cause a problem, especially if they have recently been shocked or if they use particularly high amounts of MPS.