For how long is this happening?
Do you get itchy and with rash only after swimming in pool?
How does the rash look like?

First of all is this a private pool or local city pool. That means the world of difference you know. There are other elemeints in pool sanitary cleaning then chlorine. Stuff to decompose algie etc. It could be possible there is something else in that, that is doing this to you. I would read the label on the bottle if this is your own private pool.

My son is allergic to chlorine, when we had our pool he looked like he had a sunburn every time he got out of the pool he would also have welt marks.
It eventually went away. If there's too much chlorine in the pool it can very well be the problem.
Watch out for hot tubs as well, many hot tubs have chlorine in them as well. There are other products to use in place of chlorine for hot tubs.

If this is your own pool ask the pool company what other products are available if they are available for pools as well.

As for the sunscreen it can be an ingredient in there that's adding to your rash/allergy.

I would think this allergy is due to algaecide in the pool water. Silver and copper are used and can give serious rashes that resemble measles like appearance,also exzema and cerebral irritibility.
Also another well known irritant is bromazine also used to sterilize pool water. Often its not the chlorine but other chemicals or metals.
Once you have the problem you need to go and swim elsewhere because it will only get worse if you continue exposing yourself to the irritant.
I am so allergic to most chemicals that I can only swim in chemical free(UV sterilized)pools.

I am a Learn to Swim teacher and spend up to 3 hours in pool water at 32 degrees celcius. I have developed an itchy rash over stomach and back and is now spreading to legs and arms. I have been told I have a sensitivity to warm water and that I may need desensitising. I have just been to dr and he has never heard of this condition. Could it be true or would it be allergic reaction to the chemicals in the pool. I am bathing in pinetarsol, using Egoderm cream and anti-histamines but it will not go away and is driving me crazy.

I am sure its the chemicals in the pool that are causing your problem as its so severe. After all this would have shown up before in bathing and showers if it was a reaction to warm water only.
Ask what the pool are using to sterilize the water. If its a copper based algaecide that could be the culprit. Also you could be sensitive to chlorine or any other chemical used.
My daughter is sensitive to warm water but although she goes red for a couple of hours after exposure it does not itch or leave a permanent rash. This latter is almost always associated with pool chemicals.
This is not a good prognosis for a swim teacher I am afraid.

Just a thought
Try another swimming pool and see if you get the same problem. Obviously ask what both pools are using as if its the same sterilisation chemicals you will have the same rash etc.

I started swimming in the local pool 6 months ago. In the last month I have developed a rash on several parts of my trunk - never my arms or legs. I have tried various steroid creams but it never goes completely. It is very itchy and looks like tiny pimples. Could it be the pool chemicals?

I have swum in two American pools recently and each time got a very bad outbreak of exzema. I have discovered they all use algaecide which can cause major skin irritation. However there are other irritants like chlorine and bromazine.
Once you are sensitized you will get more and more irritation each time you swim.

Many thanks for your help Serrae. I have decided to give up swimming for a month and see if the problem clears up. It is difficult here in UK to find out what they use in the public pools. No-one seems to be able to tell me so I think it best to avoid them all for a while.

Thanks for all your information, Serrae. Our pool pump/heater was not working so I wasn't in the pool/spa (3000 gal) for about 9 months. Last year I went to a dermatologist and they did all kinds of test, but obviously did not test me for pool chemicals. Just last week our pump was fixed and Bam! The itching and the rash came back. It's small raised bumps, then they turn red and dry. Arms and legs mostly. The itching is worse than any I've ever had, even poison ivy. We are draining the pool today and will attempt trial and error with remedies.

I tried loads of different chemicals in our pool and all of them gave me a problem. Bromazine,chlorine,aquasilk(worst of all for me using silver and copper ions)and in the end I bought a UV sterilizer that cleans the pool water without the use of chemicals. If the water gets a bit fuggy you are advised to use hydrogen peroxide to clear it. However in practice I have found it very difficult to buy large amouts of peroxide. Instead very occassionally I put in a half measure of chlorine.
The main problem has been algae on the pool cover. I have a smooth cover now that I can wash algae build up off. I have been using UV alone in this fashion and swim daily in the summer for over 8 years.
I only get rashes now from public/spa pools.
I hope this helps. I thought salt water pools would help me but they use algaecides which give me allergies.