Psoriasis can feel arbitrary — flaring without warning, then quietening again. It isn't. There's a genetic and immune predisposition underneath, and a fairly well-defined set of triggers on top. Knowing which is which is what turns it from baffling into manageable.
In short
A genetic predisposition plus an overactive immune response that drives skin cells to pile up. Triggers then set off flares: infections, skin injury, certain medications, smoking, stress and metabolic factors. One that's usually left off the list and matters here — stopping steroid creams abruptly. Not contagious, not your fault, and genuinely treatable.
Quick answer
Genes and immunity load the gun; triggers pull it. The predisposition sits in immune-related gene variants including the PSORS1 region. Triggers include skin injury (Koebner), strep throat (which can cause guttate psoriasis), certain medications, smoking, alcohol, stress and metabolic factors. Abruptly stopping steroids can trigger a severe flare — never stop a prescribed medicine on your own. Psoriasis is not contagious and not your fault, and modern treatment works well.
On this page
What psoriasis is
A chronic, immune-mediated condition producing thick plaques topped with silvery-white scale, most often on the scalp, elbows, knees, lower back and nails. Not contagious. It runs in flares whose timing is hard to predict, and lesions can appear at sites of skin injury — the Koebner phenomenon.
It occurs across all populations and skin tones, though on deeper skin plaques often look violet, brown or grey with greyer scale, which contributes to under-recognition and later diagnosis. Most cases are mild; a minority are severe or involve the joints as psoriatic arthritis.
The Genetic And Immune Foundation
Psoriasis runs in families, and the strongest known genetic contribution sits in the PSORS1 region, alongside other variants in immune-related genes. These tilt the immune system toward misfiring: without any infection present, immune signalling in the skin pushes keratinocytes to multiply far faster than normal, so they stack up as thickened, scaly plaques.
But genes aren't destiny. Most people with the predisposition also need a trigger for psoriasis to appear or flare — which is what "multifactorial" means in practice, and why two people with similar family histories can have completely different experiences.
External Triggers
Skin injury — the Koebner phenomenon
New plaques can form at sites of injury or friction. "Avoid skin injury" is vague, so concretely: scratches, cuts, sunburn, tattoos, insect bites, waxing and threading, tight straps and waistbands, and vigorous scrubbing all count. It's also why picking at scale is counterproductive — the trauma can extend the plaque.
Infections
The link with streptococcal throat infection is well established — strep can trigger guttate psoriasis, a shower of small drop-like spots, often in younger people and sometimes as a first-ever episode. Reassuringly, a guttate flare after a sore throat frequently settles, and it doesn't necessarily mean a lifetime of plaques.
Certain medications
Some can trigger or worsen psoriasis in susceptible people — including certain antimalarials, some blood-pressure medicines (beta-blockers, ACE inhibitors), lithium, and some treatments for hepatitis C or multiple sclerosis.
Important: if you suspect a medicine is affecting your skin, tell your doctor — but don't stop it on your own. Several of these treat serious conditions, and stopping abruptly can carry its own risks. Your prescriber can weigh the options.
Smoking and alcohol
Smoking is associated with higher risk, particularly of the pustular form, and heavy alcohol use with more severe disease and poorer treatment response. These are risk factors, not moral failings — and reducing either is genuinely useful rather than a reproach.
Sun and weather
Nuanced. For most people controlled UVB phototherapy treats psoriasis, and many notice improvement in summer — but sunburn is skin injury and can trigger Koebner plaques, so uncontrolled sun exposure isn't the same thing. A small minority have a photosensitive form that worsens with sun. Cold, dry weather commonly makes plaques worse.
The Trigger Usually Left Off The List
Corticosteroids treat psoriasis, so they rarely appear on trigger lists. Stopping them abruptly is a different matter, and it's worth knowing about.
⚠ Steroid withdrawal can trigger a severe flare
Abrupt withdrawal of systemic corticosteroids — or of potent topical steroids used extensively — is a recognised trigger for pustular psoriasis, one of the more serious forms, and for severe rebound flares generally.
Why this matters particularly here: potent steroid creams are widely available over the counter, frequently used on large areas for weeks, and then stopped suddenly — when they stop working, when the tube runs out, or when someone reads that steroids are harmful.
The safe route is a doctor-managed taper, not a hard stop. If you've been using a steroid cream regularly and want to come off it, that's a conversation to have rather than a decision to make alone — and it applies whether or not you have a psoriasis diagnosis.
Internal Factors
Metabolic health
Psoriasis is meaningfully associated with metabolic syndrome, likely through shared inflammation rather than one causing the other. Because that association also carries cardiovascular relevance, psoriasis is worth managing as a whole-body condition with a doctor rather than only as a skin one. This is about health, not fault.
Stress
Among the most commonly reported triggers, and the relationship runs both ways — flares cause stress, stress worsens flares. Managing it won't cure psoriasis, but it's a real part of the picture rather than a soft suggestion.
♡ The emotional side matters
Psoriasis is visible and widely misunderstood — people are asked whether it's catching, or judged for it. That carries a real weight, and it isn't vanity to find it hard.
If it's affecting how you feel day to day, that's worth raising alongside the skin itself — with your doctor, your dermatologist, or a mental-health professional. It's part of the condition, not a separate weakness.
What You Can Do
More control than it feels
You can't change your genes, but many triggers are manageable: treat throat infections promptly, review suspect medications with your prescriber, protect skin from injury — including waxing, threading and scrubbing — avoid smoking, moderate alcohol, look after overall health, and find something that works for stress.
And keep emollients going. Regular generous moisturising is recommended alongside treatment: it doesn't touch the immune process, but it eases scaling and discomfort, and softening scale beats scratching it off.
The Bottom Line
Psoriasis isn't caused by one thing — a genetic and immune predisposition that triggers set off. You can't change the genes, but infections, skin injury, medications, smoking, stress and metabolic health are all manageable — and one that's often missed: never stop steroids abruptly. Not contagious, not your fault, and today's treatments work.
Questions, Answered
What causes psoriasis?
A genetic predisposition plus an overactive immune response that drives skin cells to build up into scaly plaques — then triggers set off flares: infections, skin injury, certain medications, smoking, stress and metabolic factors. Genes and immunity load the gun; triggers pull it. It isn't caused by poor hygiene and isn't contagious.
Can stopping a steroid cream cause a flare?
Yes — abrupt withdrawal of systemic steroids, or of potent topical steroids used extensively, is a recognised trigger for pustular psoriasis and severe rebound flares. It matters here because potent steroid creams are widely sold over the counter, used for weeks, then stopped suddenly. If you want to come off one, ask a doctor to manage a taper rather than stopping outright.
What counts as "skin injury" for the Koebner phenomenon?
More than you'd expect: scratches, cuts, sunburn, tattoos, insect bites, waxing and threading, tight straps or waistbands, and vigorous scrubbing can all prompt new plaques at the site. It's also the reason picking at scale backfires — softening it with emollient is better than scraping it off.
Can medications trigger psoriasis?
Some can in susceptible people — certain antimalarials, some beta-blockers and ACE inhibitors, lithium, and some hepatitis C and multiple sclerosis treatments. If you suspect one, tell your doctor, but don't stop it yourself: several treat serious conditions, and stopping abruptly carries its own risks. Your prescriber can weigh the alternatives.
Does sunlight help or hurt?
Mostly helps, with a caveat. Controlled UVB phototherapy is an established treatment and many people improve in summer. But sunburn is skin injury and can trigger new plaques through the Koebner phenomenon, so uncontrolled exposure isn't the same as supervised light therapy. A small minority have a photosensitive form that worsens with sun.
Is psoriasis contagious?
No. It's immune-mediated, driven by genetics and triggers rather than infection, so it can't be caught or passed on. It isn't a hygiene issue and isn't anyone's fault — and saying so plainly matters, because the assumption that it might be catching is a large part of the stigma people with psoriasis deal with.
References
- Kamiya K, Kishimoto M, Sugai J, Komine M, Ohtsuki M. Risk factors for the development of psoriasis. International Journal of Molecular Sciences. 2019;20(18):4347. — note first author
- Rendon A, Schäkel K. Psoriasis pathogenesis and treatment. International Journal of Molecular Sciences. 2019;20(6):1475.
- Balak DMW, Hajdarbegovic E. Drug-induced psoriasis: clinical perspectives. Psoriasis: Targets and Therapy. 2017;7:87–94.
- Alexis AF, Blackcloud P. Psoriasis in skin of color: epidemiology, genetics, clinical presentation, and treatment nuances. Journal of Clinical and Aesthetic Dermatology. 2014;7(11):16–24.
- DermNet. Psoriasis; guttate psoriasis; generalised pustular psoriasis; Koebner phenomenon. dermnetnz.org
🔴🔴 Note to editor — reference 2 was visibly broken on the live page. It read "Ogawa E, Okuyama R, et al. / Ohtsuki M, et al. Risk factors for the development of psoriasis" — two citations merged with a slash, left in place. It's also the same paper flagged on the eczema-vs-psoriasis article: the correct attribution is Kamiya K, Kishimoto M, Sugai J, Komine M, Ohtsuki M, with Ohtsuki as last author. That one paper has now been misattributed three different ways across the library, which is a strong argument for a single reference-verification pass rather than page-by-page fixes. The Griffiths entry has also been replaced — Griffiths citations have proven unreliable repeatedly in this project. ⚠️🔴 Corticosteroids were missing from the medication-trigger list. Abrupt withdrawal of systemic or potent topical steroids is a recognised trigger for pustular psoriasis and severe rebound flares — it belongs on any drug-trigger list, and it matters disproportionately here because potent steroid creams are sold over the counter, used on large areas for weeks, and then stopped suddenly. Balak & Hajdarbegovic on drug-induced psoriasis has been added to support it. This is the fourth article in this batch where over-the-counter steroid misuse is the missing piece — after rosacea, tinea via the eczema page, and seborrhoeic dermatitis. Four conditions, one behaviour: that is a standalone article worth commissioning. ⚠️ Koebner made actionable: "avoid skin injury" doesn't tell anyone what to avoid, so waxing, threading, tattoos, tight straps, scrubbing and picking at scale are now named — the last being directly relevant, since scraping scale off extends the plaque. ⚠️ Sun handled with both halves: phototherapy treats psoriasis, and sunburn is skin injury that can trigger it — the article previously gave the first without the second. ✅ Retained and worth crediting: the medication warning, the non-moralising framing of smoking and alcohol, metabolic health without shaming or diet numbers, and the supportive, non-amplifying treatment of emotional impact. AquaBlur™ has been left off this page — fragrance on plaques is the wrong recommendation.
