In practice, treat the redness without understanding what sits behind it and it tends to return. So, the first task at your consultation is to work out what is driving yours. Several threads usually run together.
Blood vessels come first. In rosacea the small facial vessels over-react, dilating too easily and too often. Over time, some stay visibly open as thread veins. Sun exposure speeds all of it along, weakening vessel walls and the skin around them. Because of this, the NHS guidance on rosacea places daily sun protection near the top of the list. Genetics set the baseline: rosacea runs in families and is most common in fair skin that flushes readily. That said, it appears across every skin tone and is often missed in deeper ones.
Then there are the triggers, which do not cause redness so much as light the fuse. Of course, alcohol, spicy food, hot drinks, extremes of temperature, stress and hard exercise are the usual suspects. Still, most people learn to name their own. The skin barrier matters too. When it is compromised, by harsh products, over-exfoliation or a naturally reactive tendency, the skin loses water. It then inflames easily and flushes at the smallest provocation. An overactive immune response is also thought to play a part in rosacea. So is a tiny mite that lives harmlessly on most faces. Because ultraviolet feeds so many of these at once, a daily broad-spectrum SPF is not an optional extra. In turn, it is the habit that protects every other result.