According to my radiation oncologist, a new study has suggested that wearing deodorant/anti-perspirant is not an issue for radiation treatment (it used to be standard, I think, to tell patients not to use it if the underarm area was in the treatment field). Despite this, I have not been using it under my left arm; I think the sweat glands are not operating, anyway, which they told me would happen as a result of the radiation (wow - that means I will save 50% on my deodorant costs!).
At the beginning of treatment, I was given a special skin care cream (I think it's actually called "Special Skin Care Cream") to put on the irradiated area 4-5 times per day. Once my skin started to feel irritated, they gave me a more complicated regimen. Now, I put the cream on 2-3 times per day, and at night, I apply Pro-Shield (the same exact stuff I used to put on Bean to deal with diaper rash!), which is a sticky substance that you don't rub in. On top of the Pro-Shield, I put Adaptic strips, which are gauze strips that have been treated with some kind of greasy substance (feels a little like Vaseline). Then, on top of these, I put plain gauze bandages (not the kind that stick on). To keep all of this in place, I put on a tight-fitting tank top, which I then cover with a t-shirt to protect my sheets from all of these sticky, greasy substances.
It seems to work pretty well. It takes any sting out, and I think that the redness, which I notice is a bit more pronounced following treatment, seems to fade a bit by the next morning.
However, the left side of my chest and underarm is looking pretty ravaged. The skin seems to still be healthy - it's not like a bad sunburn where there's blistering and peeling, though I suppose that may come later - but many of the hair follicles have darkened, so I have basically a large red patch within which there are tons of darker little dots.
I do also feel the effects of the radiation internally; there is a tightening and some loss of range of motion, and some soreness (this is more occasional than constant). It's not permanent, but I'll need to stretch to get the range of motion back.
But only eight more to go!
(Edited to add: "ravaged" is a strong word to describe my skin. It's really not that bad. I think it might look startling to someone who was seeing it for the first time, but since I've been watching it gradually, it doesn't look so bad to me.)