Cat rash

We have two cats, one Calico and one Tabby mix. They are both beautiful cats and they are our babies. Recently we have noticed a funny rash type thing on their chins. First it just looked like their fur was getting darker and now there is a few little sores on their chins. Has anyone had this happen to their cat before and any suggestions? We do have a vet appt. this week, but we were just wondering...
Thanks for the feed back:o

Without seeing the cats is hard to tell you what it might be, cats do get chin pimples same as humans, pls point this out at your vet apt, they(vet) might suggest H. Udder wash, to scrub the area, keep us posted, Welcome fellow Londoner!