I know this is an old(er) topic, but I got really excited when I saw it and couldn't help myself.
I absolutely love rats. They are seriously one of the most misunderstood pets, but also one of the most rewarding, imo.
Had my first 3 rats in college. I've kinda been going with a Shakespeare name theme, and so I had a female Ophelia (Lia), female Isabella (Izzy), and a male dumbo Hamlet.
After those three had passed, I only lasted a month. My next was a rex female Rosaline.
After Rosie, I deviated into X-Men names with Logan, who was a ginger-colored dumbo male (he was an absolute sweetheart but had to be euthanized.) And then there's Magneto (Maggie) the rex female who has just a black hood. And I can't forget Ringo. Ex named him but I have "custody." He's my fat blob boy and loves to snuggle.
As far as allergies go, their claws can definitely cause major skin irritation unless you have one that is complacent enough to allow trimming and bathing.
Their saliva and urine are two other things that can cause reactions. Rats sorta mark their territory as they go, leaving a small trail of urine behind them. And believe it or not, they like to lick and give kisses.
One last issue is if you get a double-rex, which can be totally bald or just have uneven fur patches, you may not necessarily have allergies from fur, but from the skin. Most (not all) double rexes I've seen have had varying levels of skin issues, which can pose a risk for potential allergens.
Ok, so before I embarrass myself anymore by how much of a kid I am when it comes to rats, I'm just gonna stop.
TL; DR
Rats are bad@$$