What Causes Psoriasis? Genetics, Immunity and Common Flare Triggers

The underlying cause

Psoriasis develops when immune signalling becomes dysregulated in a genetically susceptible person. Inflammatory pathways involving cytokines such as tumour necrosis factor, interleukin-17 and interleukin-23 are important in plaque psoriasis. This biology helps explain why modern systemic medicines target specific immune pathways.

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The role of genetics

Psoriasis can run in families, but inheritance is not simple. Having a relative with psoriasis increases susceptibility without guaranteeing that a person will develop it. Many genes and environmental factors contribute.

Infections and immune activation

Some infections can precede or worsen psoriasis. Guttate psoriasis is particularly associated with streptococcal infection. Infection-related flares do not make psoriasis infectious or contagious.

Stress, skin injury and lifestyle factors

Emotional stress can coincide with flares for some people. Skin injury can lead to new plaques at the injured site, known as the Koebner phenomenon. Smoking and alcohol are also associated with psoriasis severity and broader health risks.

Medicines and treatment changes

Certain medicines can aggravate psoriasis in some people, and withdrawal of systemic corticosteroids is a recognised concern. Do not stop a prescribed medicine because you suspect a link. A clinician can review timing, alternatives and the risks of changing treatment.

Finding patterns without chasing every trigger

Psoriasis can flare without an obvious explanation. A short, consistent record of symptoms, infections, stress, skin injuries and medicine changes is more useful than trying to control every possible trigger. The aim is to prepare better questions for care, not to prove a cause on your own.

Some people with psoriasis develop plaques in areas where the skin has been injured. This is called the Koebner phenomenon. Cuts, friction, scratching, tattoos or sunburn can sometimes precede a new lesion. It does not mean ordinary contact makes psoriasis spread, and it does not happen after every injury.

The Koebner phenomenon

A flare may appear days or weeks after a possible trigger, and several factors can occur at the same time. Stress may increase while sleep decreases; an infection may coincide with a treatment interruption. This makes cause-and-effect difficult to establish from one episode. Looking for repeated patterns is more informative than treating every recent event as the explanation.

Triggers versus risk factors

It helps to separate a trigger from a risk factor. A trigger is something that may precede a flare in someone who already has psoriasis, while a risk factor is associated with developing psoriasis or with greater disease burden. Smoking, for example, is associated with psoriasis and broader health risks, while an infection may act as a short-term trigger for a particular flare. Neither concept means that one event explains the entire condition.

A cause and a trigger

The underlying cause of psoriasis involves genetic susceptibility and dysregulated immune signalling. A trigger is something that may precede increased disease activity in a person who already has that susceptibility. Streptococcal infection can precede guttate psoriasis, while skin injury can provoke lesions through the Koebner phenomenon. Stress, smoking, alcohol and some medicines are also discussed as modifiers, but a flare does not always have one identifiable trigger.

Medicines trigger psoriasis

Some medicines have been associated with the onset or worsening of psoriasis, including lithium, some beta blockers and antimalarial medicines. The relationship varies between medicines and individuals. A medication list can therefore be useful when a new flare is assessed, but prescribed treatment should not be stopped abruptly because it appears on an online trigger list. The prescriber can weigh the timing, benefits and alternatives.

The most useful way to think about what causes psoriasis is to separate what is well established from what varies between people. Psoriasis can change over time, and symptoms, body sites, treatment response and daily impact are not identical from one person to another. Use educational information to understand the terms you encounter and to prepare specific questions. If the pattern changes, symptoms become difficult to manage, or you are unsure whether a new symptom is related to psoriasis, a healthcare professional can assess it in the context of your history and current treatment.

Infections trigger some psoriasis flares

Infections can activate immune responses that influence psoriasis activity. The best-known example is guttate psoriasis, which can appear after streptococcal throat infection, particularly in children and younger adults. Not every sore throat causes a flare, and not every flare follows an infection. The timing and pattern matter. If a sudden widespread eruption follows an illness, that history can be useful during assessment.

The koebner phenomenon

The Koebner phenomenon describes psoriasis lesions developing in areas of skin injury. Scratches, friction, tattoos, surgical scars or sunburn can sometimes be followed by new plaques in susceptible people. This does not mean ordinary movement or touch spreads psoriasis. It is a local response to skin trauma, and it helps explain why aggressive scratching or forceful scale removal can sometimes make an affected area more troublesome.

How useful is trigger tracking?

Trigger tracking is most helpful when it stays simple. Record major events that plausibly relate to a flare, such as an infection, new medicine, significant skin injury or major period of stress. Trying to document every meal, emotion, product and weather change can create a large amount of data without revealing a reliable pattern. The aim is to notice repeated relationships and communicate them clearly, not to make yourself responsible for preventing every flare.

How mama health can support you

mama health is a free app for everything your condition asks of you, grounded in medical science and the experience of others, so you do not have to figure it out alone.

Use mama health to understand your labs in simple terms, upload and organise your health documents, find local care and specialists, and ask questions with answers grounded in medical science. You can also learn from the experiences of other people living with psoriasis, giving you practical context alongside evidence-based information.

Frequently asked questions

Is psoriasis genetic?

Genetics contribute to psoriasis susceptibility, but having affected relatives does not mean you will definitely develop it.

Can stress cause psoriasis?

Stress can trigger or worsen symptoms in some people, but it is not the sole underlying cause.

Can an infection trigger psoriasis?

Yes. Some infections can precede a flare, and streptococcal infection is particularly linked with guttate psoriasis.

Can psoriasis spread by scratching?

Psoriasis is not contagious. Skin injury from scratching can sometimes contribute to new plaques in susceptible skin.

Sources

1. American Academy of Dermatology (AAD), Psoriasis clinical guideline
2. NICE, Psoriasis: assessment and management (CG153)
3. EuroGuiDerm, Living guideline for systemic treatment of psoriasis vulgaris
4. American Academy of Dermatology, Psoriasis diagnosis and treatment