Red blotchy legs in shower?

So ever since I can remember, I get red blotchy legs when I stand in the shower. They get uncomfortable and start rashing around my knees then spreads all over my legs then to my feet. I used to think it was cause of the heat of the water but when I end up having to sit down in the shower the red blotches fade away. I’m a healthy weight so it’s not to do with my weight or anything. I also get it when standing anywhere for too long when warm. Never went to the doctor because of it but wondering if anyone else has similar experience or know why? This is a photo of my leg after a shower.