I have been getting this sore for many many months now. I traced it back to not drinking enough water.........this causes the dryness and sore and even a slight smell to it because it is a slight open sore.
I have had a similar problem, and I suggest the following: take a nice warm bath each morning, not a shower. Take a bar of IVORY soap and clean youre butt crack. Ivory soap is the only soap I have ever used that does not cause me skin problems. After the bath when you are dry, take a big wad of toilet paper, and ram it up youre butt. Make sure the tiolet paper makes contact with the sore. This contact will help the sore to dry and heal. You will probaly notice a blood spot on the toilet paper for the first few days. After that, the soreness should go away, and the sore should heal. Continue this practice to prevent future problems. Keep this area clean and dry.
You've got thrush
I have the same thing. I am told it is an allergy to spicy food.
I thought it was caused by friction because it happens whenever I'm doing a lot of sit ups and pants & boxers are rubbing there too hard.
My husband suffers from something very similar. He works in a tire re-tread plant and it gets extremely hot inside. He sweats so bad, it just runs down his back, and into his butt crack. At the very top of the crack it can sometimes get so dry it cracks and is very very uncomfortable. He puts bag balm on it, or neosporin on it. It's from the salt in his sweat drying and creating extremely dry skin. treat it with a really good moisturizer daily and it likely won't crack.
Hope this helps.