Rosacea results from a combination of immune system malfunction, genetic predisposition, and environmental triggers that together produce chronic inflammation in facial skin. There isn’t a single cause. Instead, several biological systems go wrong at once, creating a cycle of redness, visible blood vessels, and sometimes bumps or skin thickening that tends to flare and fade over time.
An Overactive Immune Response in the Skin
The most important discovery in rosacea research is that facial skin in people with the condition produces abnormal versions of a natural antimicrobial molecule called cathelicidin. Everyone’s skin makes cathelicidin to fight off infection, but in rosacea, the forms produced are different. Instead of simply killing bacteria, these altered peptides trigger inflammation, attract immune cells to the skin, and stimulate the growth of new blood vessels. When researchers injected these rosacea-specific peptides into mouse skin, the animals rapidly developed inflammation resembling the condition in humans.
The problem traces back to an enzyme called KLK5, which is overproduced across the entire outer layer of rosacea-affected skin. KLK5 processes cathelicidin into its inflammatory forms, particularly one called LL-37. In healthy skin, LL-37 is normally found only in immune cells that rush to wounds or infections. In rosacea, the outer skin layer generates it continuously, keeping the face in a state of low-grade immune activation even when there’s no infection to fight.
Mast cells, a type of immune cell found throughout the skin, play a central role in amplifying this process. They are one of the primary sources of LL-37, and their own enzymes cause blood vessel dilation and recruit additional inflammatory cells. In experiments where mice lacked mast cells entirely, injecting LL-37 into their skin did not produce rosacea-like features. When researchers stabilized mast cells with medication in normal mice, the inflammatory response dropped significantly. This confirms that mast cells aren’t just bystanders but key drivers of rosacea’s visible symptoms.
Genetics and Family History
People with rosacea are about four times more likely to have a family member with the condition than people without it. Several genes in the HLA complex, a group of genes that help the immune system distinguish the body’s own proteins from foreign invaders, appear to be involved. Variations in these genes may explain why some people’s immune systems overreact in the skin while others’ do not. Another set of genes involved produces glutathione S-transferases, enzymes that help neutralize oxidative stress. Variations in these genes could leave facial skin more vulnerable to damage from sun exposure and other environmental stressors.
That said, genetics alone don’t determine whether you develop rosacea. They set the stage by making your skin’s immune system more reactive, but triggers from your environment and lifestyle push the condition into visible flares.
Skin Mites That Multiply Beyond Normal
A microscopic mite called Demodex folliculorum lives in the hair follicles of virtually every adult’s face. In healthy skin, the average density is about 0.7 mites per square centimeter, and 98% of people without rosacea have fewer than 5 per square centimeter. In people with rosacea that includes bumps and pustules, the average jumps to roughly 12.8 per square centimeter.
These mites aren’t thought to cause rosacea on their own, but their overpopulation likely worsens it. When Demodex mites die, they release bacteria from their bodies into the follicle, which can provoke an immune response. This feeds into the same cathelicidin and mast cell pathways already overactive in rosacea skin. The relationship works both ways: the immune dysfunction may create conditions that allow mites to proliferate, and the mites in turn intensify inflammation.
Blood Vessels That Overreact
The persistent redness and flushing that define rosacea involve a signaling molecule called CGRP (calcitonin gene-related peptide). Biopsies of facial skin from people with rosacea show elevated CGRP levels compared to healthy controls. CGRP dilates blood vessels, increases blood flow, draws inflammatory cells into the area, and promotes swelling.
In healthy skin, blood vessels in the face expand briefly in response to heat or emotion and then return to normal. In rosacea, the neurovascular system overreacts. Flushing episodes are more intense, last longer, and over time the blood vessels lose their ability to fully constrict again. This is why rosacea often progresses from occasional flushing to persistent redness and eventually to visible, permanently dilated blood vessels called telangiectasia. The fact that blocking CGRP receptors reduces both flushing and chronic redness in clinical trials confirms this molecule’s central role.
Environmental and Dietary Triggers
Rosacea’s underlying biology is always present, but visible flares are often set off by specific triggers. These don’t cause the disease, but they activate the pathways already primed to overreact.
Heat is one of the most reliable triggers. Hot beverages and foods cause direct blood vessel dilation and also activate temperature-sensitive receptors in the skin that contribute to flushing and stinging. Capsaicin, the compound that makes chili peppers, cayenne, and jalapeños spicy, activates these same receptors. So does cinnamaldehyde, which is found not just in cinnamon but also in tomatoes, chocolate, citrus fruits, and certain vegetables like celery and carrots.
Other common dietary triggers include:
- Alcohol, which dilates blood vessels directly
- Histamine-rich foods like avocado, bananas, papaya, pineapple, and dried fruits
- Niacin-rich foods such as liver and chicken breast, which can cause flushing
- Dairy products and marinated meats
Sun exposure is one of the most frequently reported triggers. UV radiation damages blood vessels, increases inflammatory signaling, and breaks down collagen in facial skin over time, all of which worsen rosacea’s underlying processes.
A Possible Gut Connection
There’s growing evidence that what happens in your digestive system can influence rosacea on your face. One study found that people with rosacea have significantly higher rates of small intestinal bacterial overgrowth (SIBO), a condition where excessive bacteria colonize the small intestine. When SIBO was successfully treated, 78% of participants saw complete clearing of their skin lesions, and another 17.7% had significant improvement within a month.
The proposed explanation is that bacterial overgrowth makes the intestinal lining more permeable, allowing bacterial byproducts and inflammatory molecules to leak into the bloodstream. These circulating signals can then trigger inflammation in the skin. This doesn’t mean gut problems cause rosacea in everyone, but for some people, digestive health may be a significant contributing factor that goes unrecognized.
Why It Appears on the Face Specifically
Rosacea concentrates on the central face (cheeks, nose, chin, and forehead) because this area has unique characteristics that make it vulnerable. Facial skin has a higher density of blood vessels close to the surface, more sensory nerve endings, and a thinner barrier compared to skin elsewhere on the body. The face is also the area most consistently exposed to UV radiation, temperature changes, and wind. These features make it the perfect location for the convergence of neurovascular overreactivity, immune dysfunction, and environmental stress that produces rosacea.
Rosacea in Darker Skin Tones
Rosacea has traditionally been associated with fair-skinned people of Northern European descent, but it occurs across all skin tones. In people with darker complexions, rosacea is likely underdiagnosed because the hallmark redness and visible blood vessels are harder to see against more pigmented skin. The bumps, skin thickening, burning sensations, and eye involvement all occur regardless of skin color. If you have darker skin and experience persistent facial warmth, stinging, or bumps that come and go, rosacea is worth considering even if obvious redness isn’t visible.