Yeah i recognise that kind of rash (you've been scratchin too havent you
) I get it mainly when i hold one particular pet rat. He's rubbish at keeping his claws in check and not the best at being clean- he loves his filth.
I think its basically they've scratched you lightly with urine soaked claws. I don't mean wet or anything, but the bacteria is there. My chins have set areas they pee in, wheras the rats will just trapse through it without a care in the world. Smelly boys, but lovely none the less.
I tend to use something called sudocrem to calm it down. Its a child's anticeptic/nappyrash/post sunburn/insect bite all in one kind of cream.
Soothes the need to scratch and the lumps disappear after about 12 hours or so.
If you are prone to allergies though a scratch plus the added irritation of fur can increase your reaction even if you aren't allergic to the animal in particular. I'm violently allergic to cats and dogs, but not my rodents, but if i have a scratch/a cold or anything then go in contact with them, my reaction is twice as bad