What's a polite way to tell people you have Rosacea?

Tell them to grow up! Problem solved. Do not others control your feelings about life. No one person or group of persons should have that much control over how another person feels about their own life.
I don't mean to be rude, some people are inconsiderate towards things they don't understand, so their small minds point to something ridiculous.

I have redish skin too.. But i have never experienced or even knew about this red face people thinking you are hot for them stuff..

Something weird and new to me.. Strange indeed..

"I have rosacea"? You don't have to be rude about it.

Just tell them

My hub looks like he has a sunburn year round.

Nothing works to tone it down either. So he just lives with it.

Just tell them.
Do you have something from the doctor to help with it?

That's tough. Being red colored is embarrassing.

Just tell them it's a skin condition