What is this spot around the base of my cat's tail?

I put some water and coconut oil near the spot to spread the hair so you can see - his fur is not matted or oily.

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Here is a copy-pasta from another website that hasn't yet had anyone answer yet - this one looks MUCH busier

I noticed this as he was walking towards his food bowl today while I was doing stretches on the floor. His behaviour hasn't changed - he's still as playful and happy as ever. But he does tend to pay a bit more attention to the area with licking at times (in the past few hours he hasn't touched the area).

I don't suspect it's ringworm, but I could be wrong. With the amount I play with him and touch him, I'm almost positive I would be affected by now. I've had it before in the past (pre-pet) and I am not feeling it so I don't think it's that.

He's had acne flareups on his face a few months ago due to physical trauma caused by a broken tooth (since removed; acne disappeared with it). For some reason, could the acne be returning? Does acne even happen in this area?

Combed the area with a fine flea comb. No evidence of fleas whatsoever.

Don't suspect food allergies either; he's been on the same high-quality dry and wet food since I got him a year and a half ago.

Could it be dust or something irritating him? I haven't cleaned under the bed in a while and sometimes he like to hide under there and pounced at my socked feet lol. I vaccum about once a week since he's not a big shedder. Should I vacuum more?

His quality of life and health are normal given his energy levels - it just annoys me I've scrubbed the area with Germi-stat 4% (chlorohexidine) which was prescribed for his chin acne just to clean up the area a little bit. Hopefully it does something.  Is the area infected?

Please help in the meantime, since my vet isn't open on weekends?

It's really hard to tell from this photo. Can you describe what you're seeing?

I agree. The photo isn't sharp enough, I'm afraid. Of course, in the end, only a vet can provide you with an actual diagnosis but if you can take a clearer picture maybe someone here can tell you if their cat had something similar.

If you can get a clearer photograph it would help a lot.

Also, is it just dark spotting on the skin, or is there a raised area?  Can you describe it a bit more?

Anne is right, that a vet would need to look at your cat to give a diagnosis but if we have a bit more information it will be easier to tell if one of our cats has had something similar.