Plaque psoriasis is caused by an overactive immune system that forces skin cells to grow far too quickly. In healthy skin, cells take about 37 days to mature and reach the surface. In psoriasis, that process is compressed to just 4 or 5 days. The cells pile up faster than the body can shed them, forming the thick, scaly patches the disease is known for. About 3% of U.S. adults, roughly 7.55 million people, live with psoriasis, and the plaque form accounts for the vast majority of cases.
But the rapid skin growth is really a downstream effect. The root cause is a self-reinforcing loop of immune signaling that keeps inflammation locked in place. What kicks that loop into gear depends on a combination of genetics, environmental triggers, and lifestyle factors.
The Immune Loop That Drives It
Psoriasis is fundamentally a disease of misdirected inflammation. Specialized immune cells in the skin release signaling molecules that tell skin cells (keratinocytes) to multiply and that recruit even more immune cells to the area. The key players in this loop are two inflammatory signals: one that activates a particular class of immune cells, and another produced by those cells that acts directly on the skin.
The first signal promotes the growth and activation of a subset of T cells. Once activated, these T cells flood the skin with a second inflammatory signal that has a powerful effect on keratinocytes. It triggers them to thicken, multiply, and produce their own chemical attractants that pull still more immune cells into the skin. Those newly recruited immune cells produce more of the first signal, which activates more T cells, which release more of the second signal. The result is a feed-forward cycle: each step in the chain amplifies the next, locking the skin into a state of chronic, escalating inflammation.
This is why plaque psoriasis is persistent. Unlike a wound that heals and calms down, the inflammatory circuit in psoriasis is self-sustaining. The skin cells themselves become active participants, releasing chemicals that keep the immune response going even after the original trigger is long gone.
Genetics and Family Risk
Psoriasis runs in families. If one or both of your parents have it, your risk increases substantially. The strongest known genetic link involves a specific immune gene variant called HLA-Cw6. People who carry this variant are roughly five times more likely to develop psoriasis than those who don’t. This gene is involved in how the immune system identifies threats, and carrying the variant appears to make the immune system more prone to the kind of misdirected skin inflammation that characterizes psoriasis.
HLA-Cw6 is also associated with earlier onset. People with this gene variant tend to develop psoriasis before their late twenties. But genetics alone don’t determine whether you’ll get the disease. Many people carry the variant and never develop plaques, while others without it do. Researchers have identified over 80 genetic regions linked to psoriasis risk, most of them connected to immune regulation. The picture that emerges is one of inherited susceptibility rather than inherited certainty: your genes load the gun, but something else pulls the trigger.
Infections That Spark Flares
Strep throat is one of the most well-documented triggers for psoriasis, particularly for the initial onset. About two-thirds of people who develop guttate psoriasis (a form that often precedes or coexists with plaque psoriasis) report a sore throat one to two weeks before their first outbreak, with blood tests confirming a recent streptococcal infection.
The connection goes beyond coincidence. Strep bacteria produce proteins that are structurally similar to proteins found in human skin cells. This resemblance, called molecular mimicry, can confuse the immune system. T cells originally primed to fight the strep infection in the tonsils migrate to the skin, where they attack keratinocytes that look like the bacterial target. In people who are genetically predisposed, this misdirected immune response can ignite the inflammatory loop that sustains psoriasis long after the infection clears.
Chronic plaque psoriasis also worsens after bouts of tonsillitis. The tonsils can harbor persistent strep bacteria inside their cells, forming a reservoir of bacterial material that continuously stimulates the production of skin-homing immune cells.
Skin Injury and the Koebner Phenomenon
New psoriasis plaques can appear at sites of skin injury, even minor ones. This is known as the Koebner phenomenon, and it’s been documented since 1876. Cuts, scrapes, friction burns, sunburns, tattoos, and even surgical incisions can all trigger new lesions in people with psoriasis. The new plaques look identical to existing ones, both on the surface and under a microscope.
The practical implication is straightforward: any trauma to previously clear skin can become a new plaque site. This is why some people with psoriasis notice flares along belt lines, around bra straps, or at sites of repeated friction.
Medications That Can Trigger or Worsen Psoriasis
Several classes of medication are known to either induce psoriasis for the first time or worsen existing disease. The most strongly linked include beta-blockers (used for blood pressure and heart conditions), lithium (used for bipolar disorder), and antimalarial drugs like hydroxychloroquine. The lag time varies: beta-blockers can take up to 12 months to trigger psoriasis, lithium about 48 weeks for new cases and 20 weeks for flares, and antimalarials typically 4 to 12 weeks.
More recently, certain cancer immunotherapy drugs and some biologic medications used for other autoimmune conditions have been linked to psoriasis onset or flares, sometimes paradoxically. If you’re taking any long-term medication and notice new skin changes, it’s worth discussing the timeline with your prescriber.
How Obesity Fuels the Fire
Excess body fat doesn’t just correlate with more severe psoriasis. It actively contributes to the inflammatory environment that drives the disease. As fat tissue expands, its cells become stressed from reduced oxygen supply and shift into a pro-inflammatory state. They begin releasing the same types of inflammatory signals found in psoriasis plaques, including molecules that promote the immune loop described earlier.
Enlarged fat cells also attract a type of immune cell that, once activated, pumps out additional inflammatory molecules. These signals enter the bloodstream and reach the skin, where they can trigger or intensify psoriatic inflammation. This creates a biologically direct pathway between weight and disease severity, not just a statistical association. Weight loss has been shown to improve psoriasis outcomes, which further supports this connection.
Smoking, Alcohol, and Stress
Smoking increases psoriasis risk and makes existing disease harder to control. Nicotine and other compounds in tobacco smoke affect immune cell behavior in ways that favor the type of inflammation seen in psoriasis. The relationship is dose-dependent: heavier smoking is associated with more severe disease.
Alcohol worsens psoriasis through several pathways. It stimulates the proliferation of immune cells and the production of inflammatory signaling molecules. People who drink heavily also tend to experience more frequent skin injuries (a Koebner trigger), have higher rates of infection, and show unfavorable shifts in their T cell populations. These changes compound each other, making flares more frequent and harder to resolve.
Emotional and psychological stress is another well-recognized trigger. The American Academy of Dermatology lists both physiological and emotional stressors among the factors that can initiate or worsen psoriasis. Stress activates hormonal pathways that influence immune function, and many people with psoriasis can identify stressful life events preceding their worst flares.
Why It Becomes Chronic
The reason plaque psoriasis persists for years or decades comes back to that self-reinforcing immune loop. Unlike a one-time allergic reaction or a healing wound, the inflammation in psoriasis is designed to sustain itself. Skin cells under attack release signals that recruit more immune cells. Those immune cells release signals that make skin cells proliferate faster. The faster-growing skin cells produce even more recruitment signals. Each component of the cycle drives the others forward.
This is also why psoriasis can go into remission and then return. The genetic susceptibility never changes. The immune memory that drives the inflammatory loop can be suppressed by treatment or favorable conditions but remains ready to reactivate when a new trigger appears, whether that’s a strep infection, a stressful period, weight gain, or a new medication.