All spider bites will leave bumps, sting and itch, but the Brown Recluse is the worst in this area of the United States. The Brown Recluse secretes a necrotic venom. It's one of two in the US with a medically significant venom, the other is the Black Widow.
If you run a search on the Internet under images on Google there are numerous pictures of the horrible rash, blisters, and sores that plague the victims of a single bite from this spider.
The Brown Recluse ranges from Kentucky to Texas, but have also been found in several mid-western states so they're spreading, which may be related to warmer temperatures in the area.
A simpler answer is more likely to be interstate commerce where they travel in boxes of produce and are later carried home in grocery bags.
It can range in coloration from whitish, dark brown, to a blackish grey. An adult is about the size of a penny. If you're close enough to observe it has one strange characteristic - it has three (3) pairs of eyes unlike other spiders that have one pair.
The problem is you can find this 'house spider' almost anywhere it is dark and dry. A favorite place outside the home is in a woodpile, so be careful when you're taking wood into the house for a cozy fire.
In your home they can be anywhere, under the bed, in closets, cabinets, behind the furniture, in a chest behind and under the drawers, out-buildings, in the basement, behind books on shelves, in workshops, behind pictures, under tables, in the garage and the list can go on and on if there is a relatively undisturbed pot that is warm and dry.
Some years ago a neighbor was working in the crawl space under his house and by accident stuck his head in a nest of Brown Recluse spiders that had recently hatched.
He was able to drive home to Louisville, KY, but later in the evening he collapsed. His wife was an RN and managed to get him to the hospital.
By the time they arrived all of the major systems of his body were shutting down, thankfully the emergency room physician noticed the bite marks on his forehead and on his scalp. With antibiotics and other measures she saved his life and reversed the process. He was months healing and had to under go major rehabilitation to learn to walk, use his arms, and regain his speech.
His wife told me the doctor counted eighteen bites after his head was shaved. They were very grateful the bites were from very young spiders whose venom capacity was not fully developed.
Check around your home, use a flashlight to investigate dry dark places, remove bed skirts and move the bed out from the wall so you can vacuum behind it frequently. One measure of checking for a spider infestation in your home is to put sticky tape along baseboards to see what you can collect before you call an extermination company.
The illustration is from Google Images.