Blood on bathroom toilet seat, what can be the cause?

Hi, I was cleaning the toilet and I noticed some little tiny blood-like specks on top of the rear part of the toilet seat. (on the top back part of the U of the sitting area of the toilet seat) The only person that uses that toilet is a 58 year old male. He sits for bowel movements and also sits to urinate to avoid drops/spots of urine on the seat/floor. In other words, the top part of his buttocks and crack are touching that part of the toilet seat. What can be the causes for these tiny blood-like specks on top of the rear part of the sitting area of the toilet seat? (I don’t know if this has anything to do with the question, but he could be/is bisexual and he uses the same pair of underwear for one week. He says, he doesn’t sweat and they aren’t dirty. He only does bowel movements in the house and immediately goes into the shower to clean/bathe his buttocks.) Thank you.

Age: 62
Female
Medications: None