Other symptoms include spider veins, spots and red bumps. It's an extremely common rash affecting as many as one in 10 people, according to some estimates. The symptoms are often wrongly thought to be connected to heavy drinking, particularly if the nose is affected, and it can also be misdiagnosed as acne.
It's a condition that tends to die down and flare up from time to time, but the symptoms may become persistent and last longer the longer you have it.
Dermatologists say rosacea often begins with a tendency to blush easily and the redness persists. Symptoms include facial redness, small red bumps, pus-filled spots, dilated blood vessels (spider veins called telangiectasia). Rosacea rashes can also cause pain and a burning sensation.
Sometimes, rosacea results in thickening of the skin on the face and the nose can also become large and bulbous due to oil-secreting glands in the nose overgrowing, a condition called rhinophyma.
Other complications include red, itchy, sore eyes and a sensitivity to light and more serious eye conditions, that can affect your sight (called ocular rosacea).
Experts still don't fully understand the causes of rosacea but a number of possible explanations have been put forward.
One interesting new theory is that rosacea may be caused by having too many tiny spider mites called demodex living in your pores. We all have them but people with rosacea have been shown to have more. It's the demodex faeces which is believed to cause the skin reaction.
Another theory is that in rosacea, the immune and sensory nervous systems are all over stimulated and impaired leading to chronic inflammation.
Facial flushing and redness can sometimes also be a side-effect of prescription drugs including calcium channel blockers used to treat blood pressure and topical corticosteroids prescribed for acne flare-ups.
Rosacea does tend to run in families, but experts say there's no clear genetic link.
Lifestyle factors which can trigger rosacea attacks include hot drinks, alcohol, exercising, extremes in temperature, exposure to sunlight and spicy foods.
Your GP should be able to identify your symptoms by taking a history and examining your skin.
Who gets it?
Rosacea is more common in fair-skinned, white people (it's sometimes referred to as "the curse of the Celts") aged 30 to 50, but all races are affected. It tends to be more common in women, although the more serious rhinophyma is mainly seen in men aged over 40.
Rosacea has in the past been regarded as difficult to treat, because the causes of the redness are not understood, but more treatment options are now available.
Self-help measures include avoiding triggers such as alcohol, hot drinks and spicy food, as well as wearing a factor 30-plus sun block. Also, avoid scrubbing your face and perfumed soaps and moisturisers as they can cause irritation.
Antibiotics can help reduce rosacea spots and pimples, but do nothing to reduce the redness itself. Treatments for spots used include gels or creams containing metronidazole or oral antibiotics such as tetracycline, erythromycin and clindamycin.
Another treatment is azelaic acid gel applied twice daily, although it may cause stinging, burning or itchy, dry skin.
Brimonidine tartrate (Mirvaso®) is a newer treatment for treating facial redness. It works by causing narrowing of facial blood vessels within 30 minutes, lasts for up to 12 hours, and can be prescribed by a dermatologist.
Skin camouflage make-up is also available which can help conceal redness - you can be referred by your doctor to a professional who can teach you the techniques.
If you develop skin thickening, eye complications or severe rhinophyma you need to be referred to a dermatologist or a plastic surgeon. Treatments they can prescribe include the acne drug isotretinoin, pulsed dye laser and intense pulsed laser sessions.