You're pretty much in the same steamy hot weather I am in.
It could be scratches but it could be something else, so it's best to let the vet look at it to be sure what you're dealing with.
I deal with "your standard case of scratches" every summer because of the high humidity, on a couple of my horses.
Week ago Saturday my Arab came in with his left front ankle swollen half again its size and little bumps on top of bumps on top of bumps going up to his knee. I have never seen anything like it
I shaved his leg clear up to the knee, cold hosed him for five minutes (because that's all he could stand of the cold water), washed him up with medicated shampoo and slathered stuff on him.
While he had horrible heat in the ankle, he was not running a fever and he was not lame or sore.
Tuesday evening rolls around and the horse that grazes with the Arab came in with the same thing but on his left hind leg
I repeated the drill but this time I called the vet first thing the next morning.
We are smack in the middle of the Tennessee Walking Horse National Celebration so I hated calling because I know every vet in my county is on call at the Celebration Grounds or training barns.
Thankfully my vet knows me well enough that I don't embellish things, even if I do give him too much detail when he doesn't need it.
He didn't come out (I went and picked up something he mixed) but this is what he said:
1. It most likely was not scratches but was probably bites from some sort of ground mites or they got into ant hill.
2. He said this never-ending high heat/humidity has made this the worst year he can remember (he got his license in 1980) for scratches, bites, allergies, you name it that we don't generally have to deal with.
The special mix I picked up at his office has performed miracles in 24 hours. It looks like none of the bumps are going to shed hair, but the bumps are dieing and flaking off.
I know it's one part DMSO. His phone was cutting out, so I couldn't hear the rest but DMSO is not something I am going to experiement with to see if I can figure out the rest of the mix.
I have never in my life seen anything work this fast. He said "--the Clydesdale Folks swear by this stuff".
I washed both horses legs (all 8 legs just to be safe and because it felt good to The Boys) in really warm water and Dawn dish soap to get everything off before I sprayed the mixture on. If Dawn is good enough for the ducks in an oil spill, it's good enough for horse legs
I toweled them dry, then made them stand in front of the tub fans, but a blow dryer on cool would work too.
I donned a surgical glove, sprayed a paper towel with the stuff then gently massaged it onto the affected legs of both horses.
I figure I will be done using the stuff by this coming Tuesday.
Even if I knew the recipe, I would not put it on the net because DMSO is involved. BUT if the OP wants her vet to talk to my vet, PM me and I will give you my vet's phone number
Someone else could've said this a lot faster and got the point across - I am sorry the explanation took so long but putting disclaimers in every sentence, seems to be the Way of Today's World.