Can they sack me?

I suffer with bad eczema and my employers said they would pay the £100 excess on my company health scheme to try and get it sorted. I actually think I am suffering red skin syndrome, which is a withdrawal effect when you stop using steroid creams and I don't want to use anything steroid related. Well, I saw the dermotologist and he wants me to take steroid tablets, but I also suffer with rosacea.My own doctor has not prescribed steroids as he says it will make my rosacea worse, and I have read this online too. So I don't want to do what they suggest. Can they sack me over it?