What Causes Psoriasis? Genetics, Immune System, and Environmental Triggers Explained

Anyone diagnosed with psoriasis eventually asks the same question: why me? The honest answer is that no single cause explains every case.

The exact cause of psoriasis is unknown, but it is believed to be a combination of genetic, immune system, and environmental risk factors working together. Understanding how these three pieces interact is the best way to make sense of why psoriasis develops, why it flares, and why treatment works the way it does.

This guide breaks down each contributing factor using current research, so you can understand not just what causes psoriasis, but why it behaves the way it does in your own skin.

The Short Answer

Psoriasis is generally understood as a perfect storm of three ingredients. Genetic susceptibility sets the stage, immune system dysfunction drives the visible symptoms, and an environmental trigger is usually needed to switch the whole process on.

Crucially, having the genes for psoriasis does not guarantee you’ll develop it. About 10% of people are born with a psoriasis-related gene, yet only 2% to 3% of the population actually develops the disease, which shows just how important that third ingredient — a trigger — really is.

Psoriasis Is an Immune-Mediated Disease

At its core, psoriasis is not a problem with the skin itself. It is a problem with immune signaling that happens to show up on the skin.

An Overactive Immune Response

Psoriasis is a disease in which the immune system is triggered and mistakenly attacks its own cells and tissues. Immune cells called T cells, which normally defend the body against bacteria and viruses, mistakenly treat healthy skin as a threat.

In psoriasis, T cells attack the skin, and in psoriatic arthritis, they attack the joints instead. This is why psoriasis is classified as an immune-mediated inflammatory disease rather than a simple skin disorder.

Why Skin Cells Build Up So Fast

Normal skin cells take about a month to mature and shed. In psoriasis, skin cell turnover happens up to ten times faster than the normal rate, and the body simply cannot shed the extra cells quickly enough.

This is what creates the thick, scaly plaques associated with the disease. As a result of the immune system’s misdirected attack, the body releases cytokines and other inflammatory proteins that cause the redness, swelling, and heat seen in active plaques.

The IL-23/Th17 Pathway

Modern research has pinpointed a specific immune signaling loop behind this process. Genome-wide association studies have linked multiple psoriasis susceptibility genes to immune-related pathways, providing a clear genetic connection between psoriasis and immune dysregulation.

The central players in this loop are IL-23 and Th17 cells. IL-23 activates a signaling pathway that drives the differentiation and proliferation of Th17 cells, which then release inflammatory cytokines including IL-17, IL-21, and IL-22.

These cytokines don’t just cause inflammation in isolation; they actively drive the skin changes seen in psoriasis. These inflammatory cytokines enhance keratinocyte proliferation, stimulate blood vessel growth, and promote further immune cell infiltration into psoriatic skin, creating a self-sustaining cycle.

This discovery is not just academic. It directly explains why the newest and most effective psoriasis medications, biologics that block IL-23 or IL-17, work as well as they do.

The Genetic Link

Family history is one of the clearest, most consistent risk factors in psoriasis. If it runs in your family, your own risk is meaningfully higher than average.

How Strong Is the Genetic Component?

Family and twin studies have shown that psoriasis can run in families, and having a parent, grandparent, or sibling with psoriasis raises an individual’s chances of developing it. Identical twin studies, in particular, show far higher concordance than fraternal twins, underscoring how much genetics matters.

The Genes Involved

Researchers have made significant progress identifying which specific genes are involved. Over 80 genes related to psoriasis have now been identified, including HLA-Cw6, CARD14, and various interleukin genes that affect immune function and inflammation, and this research has directly paved the way for today’s targeted biologic treatments.

A few specific genes are worth knowing by name. HLA-Cw6 is strongly associated with psoriasis generally and especially with guttate psoriasis, IL36N is specifically linked to pustular psoriasis, and CARD14 can trigger plaque psoriasis once activated by an environmental factor.

Genes Alone Aren’t Enough

This is perhaps the most important and most reassuring part of the genetic story. In most cases, genetic changes alone are not enough to activate psoriasis; an environmental trigger also needs to be present.

You might not be able to control your genetics, but you often can identify and manage the environmental triggers that interact with them. That distinction is where the rest of this guide focuses.

Environmental and Lifestyle Triggers

If genetics and immune biology set the stage, environmental triggers are what raise the curtain. These factors vary significantly from person to person, which is part of why psoriasis can look so different across patients.

Infections

Infections are among the best-documented psoriasis triggers, particularly for certain subtypes. A triggering event, like an infection, may cause a change in the immune system that results in the onset of psoriasis symptoms, and this connection is especially strong with streptococcal infections.

The link between upper respiratory infections and guttate psoriasis is the most well-established connection of its kind, according to research published in the International Journal of Molecular Sciences. It’s possible to have strep throat with no obvious symptoms, so anyone with a psoriasis flare and no clear trigger should ask their doctor about strep testing.

Other infections have been implicated too, though less definitively. Infections, especially streptococcal and HIV infections, are recognized external factors that may increase the chances of developing psoriasis, according to the National Institute of Arthritis and Musculoskeletal and Skin Diseases.

Even viral illness in general appears to play a role for some patients. A psoriasis flare can sometimes follow an ear infection, bronchitis, tonsillitis, or another respiratory infection, since anything that activates the immune system has the potential to disturb psoriasis control.

Emerging research has also examined newer viral triggers. Emerging evidence suggests that SARS-CoV-2 may trigger new-onset psoriasis or worsen existing disease, likely through virus-induced activation of specific immune receptors that lead to inflammatory cytokine release.

Skin Injury (the Koebner Phenomenon)

Physical trauma to the skin is a well-documented and fairly reliable trigger. Well-identified triggers include trauma related to the Koebner phenomenon, along with sunburns, meaning cuts, scrapes, tattoos, and even sunburned skin can develop new plaques at the injury site roughly one to two weeks later.

Scratches, bumps, and bruises can all irritate the skin and activate the immune system, aggravating psoriasis. This is one of the more actionable triggers, since simply protecting skin from unnecessary injury is a genuinely useful, evidence-based habit.

Medications

Certain drug classes are recognized triggers or aggravating factors for psoriasis. Medications such as beta-blockers and ACE inhibitors are among the well-identified environmental triggers of psoriasis, alongside lithium and antimalarial drugs in other research.

Anyone starting a new long-term medication for an unrelated health condition should mention their psoriasis history to the prescribing doctor. This allows an informed choice between therapeutic alternatives when one exists, rather than discovering the connection after a flare.

Stress

Stress is one of the most commonly self-reported psoriasis triggers, and the relationship works in both directions. Stress is one of the most common psoriasis triggers, and at the same time, a psoriasis flare itself can cause additional stress, creating a loop that can feel never-ending.

The encouraging part of this connection is that it can be interrupted. Relaxation techniques and stress management strategies may help prevent stress from further impacting psoriasis, making this one of the more actionable triggers on this list.

Smoking

Smoking has one of the strongest evidence bases of any lifestyle trigger. In a population-based case-control study, smoking was associated with a 70% increased risk of new-onset psoriasis.

The effect doesn’t stop at onset, either. Smoking is known to promote both the onset and the maintenance of psoriasis and to reduce the response to treatment, and patients with psoriasis have been found to be considerably more likely to smoke than the general population.

Alcohol

Alcohol consumption shows a similarly consistent, if complex, relationship with psoriasis. Alcohol abuse positively correlates with psoriasis severity and reduced treatment efficacy, and is also associated with significantly increased mortality rates in people with psoriasis.

This doesn’t mean occasional drinking is dangerous for everyone with psoriasis, but heavier or long-term alcohol use appears to make disease control measurably harder. Reducing intake is one of the more evidence-supported lifestyle changes available to patients.

Obesity and Body Weight

Body weight has a well-documented, dose-dependent relationship with psoriasis risk. For each unit increase in body mass index, researchers found a statistically significant 9% increased risk of psoriasis onset and a 7% higher risk of increased disease severity.

The effect becomes even clearer at the high end of the weight spectrum. Obesity, defined as a body mass index of 30 or higher, was associated with a two-fold increased risk of psoriasis onset compared with normal body weight in the same study.

This relationship likely runs in both directions. Obesity is now recognized as an independent risk factor for both the onset and the severity of psoriasis, and researchers continue to study the underlying mechanisms connecting fat tissue, inflammation, and immune signaling.

Cold Weather and Seasonal Changes

Climate and season are frequently reported triggers, especially in colder months. Cold weather can often cause psoriasis flares due to reduced sunlight and humidity, drier indoor heating, and the added stress and illness that often accompany winter.

This pattern lines up with the biological logic behind phototherapy, one of the standard psoriasis treatments. Moderate natural sunlight tends to help many patients, while sunburn, as noted above, can trigger new plaques through the Koebner phenomenon.

The Gut and Skin Microbiome

One of the newer and more actively researched areas of psoriasis causation involves the trillions of microorganisms living in and on the body. This research is reshaping how scientists think about triggers that don’t fit neatly into “genetic” or “environmental” categories.

The Gut-Skin Connection

The gut is not just involved in digestion; it plays a major role in regulating the immune system as a whole. Roughly 70% of the immune system is found in the gastrointestinal tract, which reveals just how significant immune activity at this site can be for conditions like psoriasis.

When the balance of gut bacteria is disrupted, a condition researchers call dysbiosis, downstream effects can reach the skin. Perturbation of the gut microbiome can create a pro-inflammatory environment, triggering the release of inflammatory signals including interferon-gamma, TNF-alpha, IL-17, and IL-1-beta, several of the same cytokines already implicated in psoriasis biology.

The Skin Microbiome Itself

Beyond the gut, the skin’s own microbial community appears to differ meaningfully in people with psoriasis. Mounting evidence indicates that skin dysbiosis plays a significant role in both the development and worsening of psoriasis, through a loss of immune tolerance to the skin’s normal bacterial residents.

Interestingly, some well-known triggers may act partly through this microbial pathway. Tobacco smoke is known to alter the composition of the gut microbiome, and since the gut and skin microbiomes appear to interact, this may be one indirect way that smoking contributes to psoriasis.

Diet’s Possible Role

Diet’s connection to psoriasis is thought to run largely through this same gut-microbiome pathway rather than through any single “trigger food.” Qualitative changes to the diet may affect the intestinal microbiome, and diet-induced dysbiosis may contribute to the cytokine imbalances associated with psoriasis.

Some nutritional strategies have shown modest supportive benefit in research settings. Supplementation with polyunsaturated fatty acids, folic acid, vitamin D, and antioxidants has been studied as a possible adjunct to standard psoriasis management, though these are supportive measures rather than replacements for medical treatment.

This is an active and evolving area of research. Microbiome-targeted treatments are not yet standard care, but they represent one of the more promising future directions in understanding — and eventually treating — the root causes of psoriasis.

Why Understanding Your Triggers Matters

Not every trigger applies to every patient, and this variability is one of the more frustrating aspects of living with psoriasis. What flares one person’s skin may have no effect at all on someone else’s.

Triggers You Can’t Control

Genetics, age, and family history sit firmly outside anyone’s control. These factors explain why psoriasis can appear even in someone doing everything “right,” and why it’s never appropriate to view a diagnosis as the result of a personal failing.

Triggers You Can Influence

Many of the environmental factors discussed above are, at least partially, within your control. Smoking cessation, reduced alcohol intake, stress management, weight management, and prompt treatment of strep infections are all realistic, evidence-supported places to start.

Building Your Own Trigger Profile

Because triggers vary so much between individuals, many dermatologists recommend keeping a simple symptom diary. Tracking flares alongside stress levels, illnesses, weather, and lifestyle changes over a few months can reveal patterns that are easy to miss day to day.

This information becomes genuinely useful at follow-up appointments, helping your dermatologist refine your treatment plan around your specific pattern rather than a generic one. (For a full walkthrough of how these causes translate into treatment decisions, see our complete guide, “What Is Psoriasis? A Complete Guide to Causes, Symptoms, and Treatment.”)

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Frequently Asked Questions

Sources & References

1. HealthCentral, “Psoriasis Causes: Genetics, Environmental Triggers, and More,” 2023.
2. National Psoriasis Foundation, “Causes and Triggers” — psoriasis.org/causes.
3. Medical News Today, “Is Psoriasis Hereditary and What’s the Genetic Link?” October 2025.
4. MyPsoriasisTeam, “5 Psoriasis Risk Factors: Smoking, Genetics, and More,” May 2025.
5. National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS), “Psoriasis Symptoms, Causes, & Risk Factors,” June 2025.
6. “Roles of Infection in Psoriasis,” PMC.
7. Psoriasis.com (psoriasisSPEAKS), “What Causes Psoriasis?”
8. “Erythrodermic Psoriasis in the Context of Emerging Triggers: Insights into Dupilumab-Associated and COVID-19-Induced Psoriatic Disease,” PMC.
9. Naldi L. et al., “Excessive Body Weight and Smoking Associates with a High Risk of Onset of Plaque Psoriasis,” PubMed, 2009.
10. “The Skin Microbiome and its Role in Psoriasis: A Review,” Psoriasis: Targets and Therapy, Dove Medical Press, 2023.
11. “The Contribution of the Skin Microbiome to Psoriasis Pathogenesis and Its Implications for Therapeutic Strategies,” PMC.
12. “Risk Factors for the Development of Psoriasis,” PMC.
13. “A Review of Psoriasis, a Known Risk Factor for Cardiovascular Disease and Its Impact on Folate and Homocysteine Metabolism,” PMC.
14. “Psoriasis: Obesity and Fatty Acids,” PMC.
15. “New Horizons in the Treatment of Psoriasis: Modulation of Gut Microbiome,” ScienceDirect, January 2025.
16. “The Role of the Gut Microbiome in Psoriasis: From Pathogens to Pathology,” Journal of Clinical and Aesthetic Dermatology, February 2025.

This article is intended for general educational purposes and does not replace personalized medical advice. Anyone with symptoms suggestive of psoriasis should consult a board-certified dermatologist for an accurate diagnosis and individualized treatment plan.