If you’ve ever asked what causes psoriasis, here’s the short answer: it’s not really about your skin. It starts with your immune system.
The red, scaly patches show up on the surface. But the real cause is happening underneath. Certain immune cells are misfiring, and your skin is just where you see the result.
This matters for treatment. Moisturizers and creams can calm a flare. But they don’t stop psoriasis from coming back, because they aren’t treating the actual cause. Here’s what is.
Your Immune System Is Attacking Your Own Skin
Psoriasis is an autoimmune disease. That means your immune system mistakes healthy skin cells for a threat and attacks them, even though there’s nothing to fight off.
A group of immune cells called T-cells lead this attack. In someone with psoriasis, these T-cells become overactive. They send out chemical alarm signals, and once that alarm starts, it doesn’t easily turn off.
Think of your immune system as a security team patrolling your skin. In psoriasis, part of that team gets stuck sounding a false alarm, over and over, with no real danger to respond to.
The alarm signals are called cytokines. You can think of them as walkie-talkie messages that immune cells use to talk to each other. Two matter most in psoriasis:
- IL-23 acts like a supervisor. It tells a specific group of T-cells (called Th17 cells) to switch on and multiply.
- IL-17 is the message those T-cells send out next. This is the one that hits your skin directly.
When IL-17 reaches your skin cells, it tells them to grow much faster than normal. It also tells them to skip steps they’d normally go through to mature properly.
A typical skin cell takes about a month to form, rise to the surface, and shed. In psoriasis, that whole process can shrink down to just a few days. Skin cells pile up faster than your body can shed them. That pileup is what you see as thick, scaly plaques.
This IL-23/IL-17 signal is so well understood now that most modern psoriasis medications work by blocking one of these two messengers directly. When you block the signal, the plaques improve. That’s strong evidence the immune system is really driving this.
Genetics Load the Gun
Psoriasis runs in families, but not in a simple way. Researchers have found over 60 regions of DNA linked to a higher risk of psoriasis. Most of them involve genes tied to that same immune pathway described above.
A few things worth knowing:
- If one parent has psoriasis, a child has roughly a 10% chance of getting it.
- If both parents have it, that risk rises to around 50%.
- About a third of people with psoriasis have a relative with it too. But plenty of people develop it with no family history at all.
- One gene, HLA-Cw6, is strongly linked to psoriasis that starts younger, often tied to strep throat as a trigger (more on that below). Another, CARD14, can trigger plaque psoriasis on its own once something in the environment sets it off.
The honest summary: genetics loads the gun, but something else usually pulls the trigger.
Triggers: What Pulls the Trigger
This is the part most people actually want to know. What sets off a flare, or causes psoriasis to show up for the first time?
According to the National Psoriasis Foundation, triggers vary a lot from person to person. The most common ones are:
- Skin injury. A cut, scratch, sunburn, bug bite, or even a vaccination can cause new plaques to form at that exact spot, days or weeks later. This is called the Koebner phenomenon. It happens in roughly a quarter of people with psoriasis, and it shows just how reactive the skin’s immune response can be.
- Infections, especially strep throat. This is one of the best-documented triggers, particularly for guttate psoriasis (a form that shows up as small, drop-shaped spots) in children and teens. One theory: the immune system’s response to strep bacteria cross-reacts with proteins in the skin. It’s a case of mistaken identity that keeps the alarm going after the infection clears.
- Stress. Stress can trigger a flare, and a flare can itself be stressful. That can create a frustrating cycle. Stress management is one of the few triggers people have real influence over.
- Certain medications. Lithium, some blood pressure medications (beta-blockers), and antimalarial drugs can trigger or worsen psoriasis in some people.
- Cold, dry weather. Less sunlight means less natural vitamin D. Vitamin D helps regulate immune activity in the skin, which is part of why psoriasis often flares more in winter.
- Smoking and heavy alcohol use. Both are linked to more frequent and more severe flares.
None of these triggers cause psoriasis in someone who wasn’t already prone to it genetically. What they do is flip a switch in an immune system that was already set up to overreact.
Why This Matters for How You Treat It
Psoriasis starts with immune signals, not dry skin. So a good moisturizing routine is still worth doing — a cream formulated specifically for psoriasis and seborrheic dermatitis can help calm itching and flaking — but it doesn’t fix the underlying immune process.
That’s why dermatologists usually treat psoriasis on two tracks: something that supports the skin day to day, and something that addresses the immune signaling itself. That second track might be a topical treatment, phototherapy, or a biologic medication, depending on how severe the psoriasis is.
When to See a Dermatologist
Psoriasis can look different from person to person. It’s sometimes confused with other skin conditions, like eczema or dandruff. See a dermatologist if:
- You’re not sure whether what you’re seeing is psoriasis, eczema, or something else
- Plaques are spreading, painful, or covering a large area of your body
- You notice joint pain or stiffness along with skin symptoms (this can be an early sign of psoriatic arthritis, which affects up to 30% of people with psoriasis)
- Over-the-counter products aren’t helping after a few weeks of consistent use
A proper diagnosis matters. Psoriasis treatment is genuinely different from eczema treatment, even though the two conditions can look similar on the surface.
Mike Marenick is the founder of HealFast Skincare and holds the patent for his invention, Ovasome Technology, used in skincare formulations. He began developing skincare products after watching his mother manage psoriasis for decades, and has spent over twenty years formulating treatments for chronic skin conditions. His work has been featured on Home Shopping Network, in two national infomercials, and in more than 300 publications including Vogue, Newsweek, and Allure. He is not a medical doctor — always consult a dermatologist for diagnosis and treatment of skin conditions.
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