Cellulitis

Yes indeedy, I've had that too but mine was caused by lymphoedema in my arm. I was warned from the outset that cellulitis is a risk with lymphoedema if you get a scratch or cut, as my lymph nodes don't work very well, but had never had a problem in nearly five years - so was possibly a bit blasé! Didn't realise what had turned my arm red - not very sore, but looked like a bad case of sunburn. Finally twigged, off to the GP and even though it was starting to recede, straight onto antibiotics. Standard treatment. I had no cut or scratch but had recently had a manicure - apparently that can easily do it if you are susceptible, and may be in no way due to lack of cleanliness by the operator, just pushing back cuticles can open up the area to germs! In your case it may have been caused by bra or clothing rubbing and leaving an opening for enterprising germs  (the cleanest clothes may still carry some bacteria, nothing much you can do).  Mine cleared up very fast, no residual problems but I'll be careful about manicures in the future. If your radiation burns are healed, you can reasonably expect to be OK and may not ever get it again.  But when you know what it is you are better prepared. My GP has given me a prescription so that if I get it again, I can start treatment immediately. If left untreated it can become dangerous. A persistent seroma caused a horrible infection four years ago, I had no indication of what might be wrong apart from feeling awful and ended up in hospital for a week on a drip of heavy duty antibiotics. I'm not keen on taking antibiotics lightly, but thank heavens for them when you really need them - the infection I got then would probably killed me if I had lived 100 years ago! Best wishes.