Rash-like condition on Buttocks and Inner Thighs

[CityHunter]

I've been trying to identify the type of rash that I have.  Here's what I've noticed:
1. It occurs much more frequently (almost always) if I run in jeans.
2. It sometimes occur if I run in running shorts, but a lot less frequently than in jeans
3. It's been happening for 10+ years now.
4. There's never any bleeding.
5. There's no distinct pattern
6. It seems to occur more frequently if I run in dry weather
7. It's not one giant patch, but several small ones
8. The size of each area can be as small as a dot to as big as a quarter (usually the size of a dime or smaller)
9. I recently saw one on the side of my belly
10. If I don't run for a few days, the redness will subside, and heal up like a scar would
11. It's slightly elevated
12. The rash is worse if I was running fast
13. Sometimes the rash would itch a bit, but for the most part, I don't really feel it.

I've checked pictures of jock itch, eczema, folliculitis, and several other common rash/skin conditions, but none of them resemble what I have.  

I really don't think this is an urgent medical condition since I've had no problems with it for 10+ years.  It's been okay as long as I avoid running in jeans.  I feel that it's happening a bit more frequently recently, not sure if it's due to the dry/cold weather.

Any tips would be appreciated.

Thanks.

[CityHunter]

Sorry for the late reply, but I've looked up many pictures of skin chafing, and I don't think that's what I'm experiencing.  When I said running in jeans, I don't actually mean a long run, but maybe just running to get the door when it rings, or something like that.  And some of the areas that have this problem are covered by my boxer.

To add a bit more details, it usually starts out as a red dot, kind of like a pimple, then it would get bigger (i think depending on how much running I did or how much contact it gets).  It is elevated at first, then it'll smooth out, but leave a dark patch (like a scar?) then it'll fade over time.

There is absolutely no abscess or discharge of any type.  I don't think it's any type of fungal infection.  

Of all the pictures I've seen so far... I think what I have is some form of rash.  But I don't quite know the cause behind it... Is it possible to get a rash from wearing boxers in general?

[AverageJoe88888]

As stated above, do not run in jeans. There is a reason people running track or jogging down the street do not wear jeans while doing so. You have some skin chafing going on. Its common in both thighs and buttocks. Running in any material not suitable for running in will cause this, as well as a possible sensativity to a certain material or detergent, wearing too tight of pants / underwear, or being overweight. There are other causes, but one or more of the above mentioned is likely your issue. Its no biggie, my husband has always had it on his rear and I have seen several others with this issue. Try correcting any issues with anything I have suggested, and if it doesnt go away, its purely cosmetic and you will be fine.

[kidnurse]

Do not run in jeans.  I don't know why you would anyway.  Do you neverhave problems with jeans, unless you run?