Psoriasis flares are set off by a wide range of triggers, from infections and skin injuries to stress, medications, and seasonal changes. Around 43 million people worldwide live with psoriasis, and for most of them, identifying personal triggers is one of the most effective ways to reduce the frequency and severity of flare-ups. The tricky part is that triggers vary from person to person, and several often overlap at once.
Stress and Emotional Pressure
Stress is the trigger patients recognize most. In survey data, 61% of people with psoriasis said they strongly believe stress contributes to their flares. The connection isn’t just psychological. When you’re under stress, your body releases adrenaline and related hormones that activate inflammatory signaling pathways, increasing circulating levels of key inflammatory molecules like IL-6 and IL-1β. These are the same molecules already elevated in psoriatic skin. Stress also reduces the effectiveness of your body’s built-in anti-inflammatory system, essentially loosening the brakes on immune activity that’s already overactive.
The effect can be cyclical: stress triggers a flare, visible skin symptoms create more stress, and that stress fuels further inflammation. Breaking the cycle often requires addressing both the skin and the stress itself.
Skin Injuries and the Koebner Phenomenon
New psoriasis plaques can form directly at the site of a skin injury, a response known as the Koebner phenomenon. Cuts, scrapes, sunburns, tattoos, bug bites, and even friction from tight clothing can all set it off. What happens is that damage to the outer skin layer disrupts the skin’s protective barrier, which launches an inflammatory chain reaction that spreads into deeper tissue. Immune cells in the area release a surge of inflammatory signals, and new blood vessel growth at the injury site feeds the developing lesion.
The process unfolds over days to weeks. Molecular changes begin within 24 hours of the injury, with inflammatory markers rising sharply between days three and seven and peaking around the second week. This means a small cut today could become a visible psoriasis plaque one to two weeks later. Not everyone with psoriasis experiences the Koebner phenomenon, but if you’ve noticed plaques appearing at injury sites before, protecting your skin from unnecessary trauma becomes especially important.
Infections, Especially Strep Throat
Streptococcal throat infections are the classic infectious trigger for psoriasis, particularly for guttate psoriasis, a form that appears as small, drop-shaped spots scattered across the torso and limbs. This type often shows up in children and young adults two to three weeks after a strep infection. The mechanism involves a case of mistaken identity by the immune system: proteins on the strep bacteria closely resemble proteins in skin cells, so the immune response aimed at the infection spills over into an attack on the skin.
Strep isn’t the only infection that matters. Upper respiratory infections, perianal strep infections, and HIV have all been linked to psoriasis flares. The common thread is that any significant activation of the immune system can push an already primed inflammatory response past its tipping point.
Medications That Provoke Flares
Several common drug classes can trigger new psoriasis or worsen existing disease. The strongest associations are with beta-blockers, lithium, antimalarial drugs, NSAIDs, and tetracycline antibiotics.
- Beta-blockers, prescribed for high blood pressure, anxiety, and glaucoma, can trigger flares through both oral and topical forms. Some cases have involved a shift from standard plaque psoriasis to more severe pustular forms.
- Lithium, used for bipolar disorder, causes psoriasis-like skin eruptions in an estimated 3% to 45% of patients, including people with no prior history of the disease. The wide range reflects differences in dosing and individual susceptibility.
- Antimalarials like chloroquine and hydroxychloroquine are widely acknowledged to induce or worsen psoriasis.
- Tetracycline antibiotics triggered flares in about 4% of psoriasis patients in one study.
- NSAIDs, common over-the-counter painkillers, also carry a recognized risk.
If you start a new medication and notice your skin worsening within days to weeks, the drug itself may be the cause. Don’t stop a prescribed medication on your own, but do flag the timing with your prescriber.
Cold Weather and Low Humidity
Many people with psoriasis notice their worst flares in fall and winter. Two factors converge during colder months. First, low humidity damages the skin’s barrier function, making the outer layer more vulnerable to mechanical stress and triggering the kind of epidermal overgrowth that defines psoriasis plaques. Second, less sunlight means less natural UV exposure. UV radiation suppresses the overactive immune pathways involved in psoriasis, promotes vitamin D production in the skin, and encourages the death of excess skin cells in lesions. When you’re bundled in heavy clothing with little skin exposed to weak winter sunlight, you lose all of those benefits.
There’s no established ideal humidity level for psoriasis, but using a humidifier indoors during dry months and seeking brief, safe sun exposure (or asking about phototherapy) can help offset seasonal worsening.
Hormonal Shifts
Estrogen appears to have a protective effect on psoriasis, which means any life stage where estrogen drops can spell trouble. The pattern is clearest around pregnancy and menopause.
During pregnancy, 55% of patients experience improvement in their psoriasis, with skin clearing most dramatically between weeks 10 and 20 of gestation. Among those with significant skin involvement, affected areas decreased by nearly 84% on average. The improvement tracks closely with rising estrogen levels, specifically the ratio of estrogen to progesterone. But the postpartum period tells the opposite story: 65% of patients see their psoriasis worsen after delivery, as estrogen plummets.
Menopause follows a similar logic. In one study, 48% of menopausal women experienced worsening psoriasis, while only 2% improved. The drop in estrogen that defines menopause removes a natural brake on the inflammatory molecule TNF-α, which is one of the central drivers of psoriatic inflammation. High estrogen levels inhibit TNF-α production; low levels allow it to surge.
Smoking
Smoking has a clear, dose-dependent relationship with psoriasis risk. A large genetic analysis (Mendelian randomization study) found that people who have ever smoked have 46% higher odds of developing psoriasis compared to never-smokers. Each additional cigarette per day raises the odds further, with a 38% increase associated with heavier daily smoking. When researchers looked at cumulative lifetime smoking exposure, the odds nearly doubled. These figures reflect a causal relationship, not just a correlation, meaning smoking itself drives the increased risk rather than some shared underlying factor.
Interestingly, the same study found no causal link between alcohol consumption and psoriasis, though alcohol may still worsen symptoms indirectly by interfering with treatment adherence or by affecting liver metabolism of medications.
Excess Body Weight
Obesity and psoriasis share a two-way relationship. Fat tissue is not just storage; it’s an active source of inflammatory molecules. Adipose tissue releases TNF-α, IL-6, and IL-1β, the same inflammatory signals elevated in psoriatic skin. It also produces hormones called leptin and chemerin that are positively correlated with both BMI and psoriasis severity scores. The more fat tissue you carry, the higher these signals climb, and the worse psoriasis tends to behave.
This means that weight gain can push psoriasis activity higher even when other triggers are absent, while weight loss can lower the baseline level of inflammation feeding your skin disease.
Why Triggers Stack Up
In practice, flares rarely come from a single trigger in isolation. A stressful month at work might not cause a flare on its own, but combine it with a winter cold, weight gain over the holidays, and dry indoor air, and you’ve created the conditions for a significant outbreak. Tracking your personal triggers over time, even informally, helps you spot patterns. Some people flare reliably with infections, others with stress or seasonal changes. Knowing your specific vulnerabilities lets you intervene early, whether that means moisturizing more aggressively in winter, managing stress proactively, or alerting your doctor when you start a new medication.