Plaque psoriasis develops when your immune system mistakenly attacks healthy skin cells, causing them to multiply far faster than normal. It’s not something you “catch” from another person or from poor hygiene. Instead, it results from a combination of genetic predisposition and environmental triggers that activate an overdriven immune response. About 3% of American adults live with psoriasis, and plaque psoriasis is the most common form.
What Happens Inside Your Skin
Healthy skin cells take about a month to grow deep in the skin, rise to the surface, and shed. In plaque psoriasis, that entire cycle compresses into just days. The result is a pileup of skin cells on the surface that forms the thick, raised, silvery-scaled patches the condition is known for.
The root cause is an immune system malfunction. Certain white blood cells become activated and release signaling molecules that tell skin cells to multiply rapidly. Those same signals also recruit more immune cells to the area, creating a self-reinforcing loop of inflammation. The skin cells keep proliferating, the immune cells keep arriving, and the plaques persist or grow. This is why psoriasis is classified as an autoimmune condition: your body’s defense system is driving the damage.
Genetics Set the Stage
You don’t inherit plaque psoriasis directly, but you can inherit a genetic vulnerability that makes it far more likely. The strongest known genetic link involves a specific immune system gene variant called HLA-C*06:02. Carrying just one copy of this variant increases your risk of developing psoriasis roughly fivefold. It accounts for more than 6% of the overall variance in disease risk, which is substantial for a single gene.
If one parent has psoriasis, your chances of developing it are higher than someone with no family history. If both parents have it, the risk climbs further. But genes alone aren’t enough. Many people carry susceptibility genes and never develop the condition. Something in the environment typically needs to flip the switch.
Common Triggers That Start or Worsen Flares
For people with a genetic predisposition, a range of triggers can set off the first outbreak or cause existing plaques to worsen.
Infections: Strep throat is one of the most well-documented triggers, particularly for a first episode in younger people. The infection appears to activate the immune pathway that leads to skin cell overproduction.
Skin injury: Psoriasis can appear at the exact site of a wound, scratch, sunburn, tattoo, piercing, or even an insect bite. This is called the Koebner phenomenon, where new plaques form in areas of skin trauma. Any injury that penetrates past the outermost skin layer can trigger it, including surgical wounds and even scratching from another skin condition.
Stress: Emotional and physical stress are among the most commonly reported triggers for flares. Stress hormones influence immune function, and many people notice their first outbreak or a significant worsening during high-stress periods.
Certain medications: Several drug classes are known to induce or aggravate psoriasis. Beta-blockers affect about 20% of psoriasis patients who take them. Lithium triggers flares in roughly 50% of psoriasis patients using it. Antimalarial drugs, common anti-inflammatory painkillers like aspirin, ACE inhibitors (used for blood pressure), and certain antifungal medications can also provoke plaques. If you’re already predisposed, starting one of these medications can sometimes be the event that first brings psoriasis to the surface.
Lifestyle Factors That Raise Your Risk
Beyond genetics and triggers, three modifiable factors significantly influence whether psoriasis develops and how severe it becomes.
Body weight: Obesity (a BMI of 30 or higher) doubles the risk of developing plaque psoriasis compared to normal weight. Even incremental weight gain matters: for every one-point increase in BMI, the risk of psoriasis onset rises about 9%. Fat tissue is metabolically active and produces inflammatory compounds, which may feed the same immune pathways that drive psoriasis.
Smoking: Current smokers face about a 70% higher risk of developing plaque psoriasis than nonsmokers. Smoking increases systemic inflammation and alters immune cell behavior, both of which can push a genetically susceptible person toward their first outbreak.
Alcohol: Heavy drinking is associated with increased psoriasis risk, though the data is stronger for men than for women. Alcohol can also interfere with treatment effectiveness, making existing plaques harder to manage.
When It Typically Appears
Psoriasis can start at any age, but it tends to follow a bimodal pattern with two peak windows. The first and more common peak is between ages 20 and 30. A second, smaller peak occurs between ages 50 and 60. Early-onset psoriasis (before age 40) tends to have a stronger genetic component and is more closely linked to the HLA-C*06:02 gene variant. Late-onset psoriasis is more often triggered by environmental factors or medications.
Children can develop psoriasis too, often after a strep infection. Men and women are affected at roughly equal rates.
How Plaque Psoriasis Looks Different From Eczema
Because both conditions cause red, irritated skin, people sometimes confuse plaque psoriasis with eczema. Plaque psoriasis produces thicker, more clearly defined patches with sharp borders and silvery-white scales. It favors the extensor surfaces of the body, particularly the outsides of the elbows and knees, as well as the scalp and lower back. Eczema, by contrast, tends to appear in skin folds (the insides of elbows and behind the knees), has less defined borders, and is more likely to ooze or crust rather than form thick scales.
A dermatologist can usually distinguish the two on sight. In ambiguous cases, a small skin biopsy provides a definitive answer.
Why It Doesn’t Go Away on Its Own
The self-reinforcing nature of the immune loop in psoriasis is why the condition is chronic. Overactive immune cells signal skin cells to multiply. Those multiplying skin cells release more signals that attract additional immune cells. Without treatment to interrupt this cycle, plaques persist. Some people experience periods of remission where plaques fade, only to have them return when a new trigger appears.
Plaque psoriasis is not contagious. You cannot give it to someone else through touch, sharing items, or any other form of contact. It is an internal immune process, not an infection.