How psoriasis severity is measured
Dermatologists use a scoring system called the Psoriasis Area and Severity Index (PASI) to measure how much of your body is affected and how inflamed the skin is. A PASI score above 10, or involvement of more than 10% of body surface area (roughly the size of both arms), typically indicates moderate-to-severe disease. Your doctor may also use the Dermatology Life Quality Index (DLQI) — a questionnaire about how psoriasis affects your daily life. A DLQI score above 10 means psoriasis is significantly impacting your quality of life, which can qualify you for stronger treatments even if your skin score alone is lower.
According to the joint AAD-NPF guidelines, approximately 80% of people with psoriasis have mild-to-moderate disease that can be adequately controlled with topical treatments applied to the skin. The remaining 20% need systemic treatments — medicines that work throughout the body.
PASI 0PASI 10PASI 20PASI 72 (max)
Mild
PASI <10
Less than 10% of body surface area affected. Plaques typically localised — elbows, knees, scalp.
First-line
Topical creams and ointments
Moderate
PASI 10–20
10–20% affected, or significant quality of life impact (DLQI >10) even at a lower skin score.
First-line
Systemic tablets or UV light therapy
Severe
PASI >20
More than 20% affected, or moderate disease not responding to systemic treatment.
First-line
Biologic injections (IL-17, IL-23, TNF inhibitors)
PASI = Psoriasis Area and Severity Index (0–72 scale). DLQI = Dermatology Life Quality Index. Your dermatologist uses both scores together — life impact can qualify you for stronger treatment even with a lower PASI score.
Mild psoriasis: topical therapy
Mild
Corticosteroids, vitamin D analogues and topical calcineurin inhibitors
First-line treatment for mild psoriasis. Topical corticosteroids (such as betamethasone — a cream or ointment applied directly to the skin) are the most widely used therapy. Around 86% of psoriasis patients receive topicals at some point. They reduce inflammation quickly but are recommended for short-term use (4–8 weeks) because prolonged use can thin the skin (skin atrophy) or cause it to stop responding as well over time (tachyphylaxis). Vitamin D analogues (calcipotriol/calcipotriene) slow down the overproduction of skin cells that causes plaques (keratinocyte proliferation) and are recommended by both the AAD and NPF as effective alternatives or complements to corticosteroids. Topical calcineurin inhibitors (tacrolimus, pimecrolimus) are preferred for sensitive areas such as the face, skin folds, and genitals where steroid creams carry a higher risk of thinning the skin.
The most evidence-supported approach for mild-to-moderate disease is the fixed-dose combination of calcipotriol and betamethasone dipropionate (FDA-approved in 2006). A meta-analysis of randomised controlled trials found that combination therapy increased the likelihood of clearance by 20–22% compared to either agent alone. Patients in the combination arm also maintained remission significantly longer.
Where lifestyle matters
At the mild stage, topical therapy alone controls most cases. Gut health, stress, and sleep are among the lifestyle factors research has associated with flare frequency. Whether addressing these alongside topicals influences disease course remains an area of ongoing research.
Moderate psoriasis: systemic therapy
Moderate
Methotrexate, apremilast and phototherapy
Methotrexate (MTX) has been a cornerstone of psoriasis treatment since 1972. It works by slowing down the rapid skin cell turnover that causes plaques and calming the overactive immune response — through a combination of anti-inflammatory, antiproliferative, and immunosuppressive effects (including inhibiting dihydrofolate reductase and promoting T cell apoptosis). Real-world data shows an average PASI score reduction of 51.2% after six months, with the effect remaining stable for up to four years. Apremilast, a tablet approved in 2014, works differently — it targets an enzyme called PDE4 (phosphodiesterase-4) that regulates inflammation signals, offering a generally well-tolerated oral option without the need for the regular liver monitoring (hepatotoxicity screening) required with methotrexate. Narrowband UVB phototherapy uses a specific wavelength of ultraviolet light to slow skin cell overproduction and is effective without affecting the whole immune system. Acitretin, a vitamin A–derived tablet (oral retinoid), is used alone or combined with light therapy, particularly for certain psoriasis variants.
Methotrexate is also used alongside biologics in some cases and remains widely prescribed globally due to its low cost and long track record. It should always be taken with folic acid to reduce the risk of nausea and mouth sores, and regular blood tests to check liver health are required during treatment. Current guidelines position methotrexate as the primary first-line systemic therapy before moving to biologics. Importantly, methotrexate must not be taken during pregnancy — it is teratogenic (harmful to a developing baby) and requires reliable contraception in both men and women during treatment and for a period afterwards. Acitretin also cannot be taken during pregnancy and requires reliable contraception for at least three years after stopping — your doctor will discuss both of these requirements in detail if either medicine is being considered.
Where lifestyle matters
Obesity is a documented predictor of reduced methotrexate and biologic efficacy. Physical activity and weight management are associated with better treatment responses in research literature. Studies on the gut-body-mind connection suggest that systemic inflammation associated with gut dysbiosis may be linked to variation in treatment response.
Newer oral option: deucravacitinib (TYK2 inhibitor)
Oral — Moderate to Severe
Deucravacitinib (Sotyktu) — TYK2 inhibitor
Deucravacitinib was approved by the FDA in September 2022 as the first oral medicine of its kind — a TYK2 inhibitor — for adults with moderate-to-severe plaque psoriasis. TYK2 is a signalling protein your immune system uses to activate the inflammatory pathways that drive psoriasis. By blocking TYK2 very precisely, deucravacitinib damps down the inflammation signals responsible for plaques without broadly suppressing the whole immune system, as older medicines tended to do. In clinical trials, nearly 60% of patients achieved at least 75% skin improvement (PASI 75) at 16 weeks, with results improving further by 24 weeks and maintained over two years. In March 2026, the FDA also approved it for adults with active psoriatic arthritis. Its once-daily tablet form makes it an important option for people who prefer not to use injections. As with all systemic treatments, your dermatologist will assess whether it is suitable for you.
One reason deucravacitinib is considered an advance over older oral options is that it works very selectively on TYK2 — it does not broadly suppress the immune system in the way that some older JAK inhibitor medicines do. This selectivity is associated with a cleaner safety profile in trials to date. It may also be a useful option for people with inflammatory bowel disease who cannot take IL-17 biologics. Clinical data confirm consistent results over two years. As always, your dermatologist will assess your full medical history before prescribing.
Severe psoriasis: biologics
Severe
IL-17 inhibitors, IL-23 inhibitors, and TNF inhibitors
Biologics are medicines made from living cells that target specific proteins (cytokines) in the immune system responsible for psoriatic inflammation — rather than broadly suppressing immunity the way older drugs do. They are used when topical and conventional tablet treatments have not worked sufficiently, or when disease severity warrants earlier escalation. IL-23 inhibitors (risankizumab, guselkumab, tildrakizumab) and IL-17 inhibitors are both considered preferred first-line biologics per current major guidelines. IL-23 inhibitors block a key signalling protein called IL-23 that keeps the inflammatory cycle going (sustaining the Th17 loop), offering durable long-term skin clearance with infrequent injections — often once every 8 to 12 weeks. In the 2024 network meta-analysis, IL-23 inhibitors demonstrated the highest rates of near-complete skin clearance overall. IL-17 inhibitors (secukinumab, ixekizumab, bimekizumab) target a different inflammatory protein called IL-17 (interleukin-17) and typically clear skin faster — making them a preferred choice when rapid clearance is the priority. Bimekizumab, approved in 2023, blocks two closely related forms of IL-17 (IL-17A and IL-17F) simultaneously, which may give it an edge over earlier IL-17 medicines. TNF inhibitors (adalimumab, infliximab, etanercept, certolizumab) were the first generation of biologics and remain effective, particularly when psoriatic arthritis is also present. Ustekinumab targets both IL-12 and IL-23 and is now generally considered second-line given the superior results seen with newer agents. Cyclosporine is an older immunosuppressant reserved for short-term control of severe acute flares and is not suitable for long-term use due to its effects on the kidneys (nephrotoxicity).
A 2024 systematic review and network meta-analysis of over 15,000 patients across 30 randomised controlled trials found IL-23 inhibitors demonstrated the highest rates of near-total or complete skin clearance among all biologic classes, followed by IL-17 inhibitors. TNF inhibitors showed lower clearance rates but have the longest track record and remain a well-established option, particularly for people with cardiovascular conditions.
The right biologic for you depends on your individual situation — including other health conditions, whether your joints are affected, and which treatments you have tried before. For example, people with inflammatory bowel disease (IBD) are generally advised to avoid IL-17 inhibitors, as blocking IL-17 can worsen IBD. People with severe heart failure may need to avoid TNF inhibitors. Cyclosporine is sometimes used as a short-term bridge during very severe flares while waiting for a biologic to take effect, but long-term use carries risks to the kidneys (nephrotoxicity) and blood pressure. These are decisions your dermatologist will guide you through.
Where lifestyle matters most
Excess body weight is associated with reduced effectiveness of TNF inhibitors and higher risk of a biologic stopping working over time (secondary biologic failure). Psychological stress activates inflammatory proteins in the blood (cytokines including TNF-alpha and IL-17) — the same pathways targeted by biologics. Research suggests that managing sleep, stress, and gut health alongside biologic therapy may be relevant to overall disease activity, though individual responses vary.
Biosimilars: lower-cost alternatives to biologics
Biologics are expensive — sometimes tens of thousands of euros or dollars per year. Biosimilars are medicines that work the same way as an approved biologic but are made by a different manufacturer after the original drug's patent expires. They go through rigorous testing to confirm they are just as safe and effective as the original. For psoriasis patients, this is meaningful: biosimilars are making treatments that were once out of reach financially substantially more affordable.
Biosimilars
What's available now
Multiple adalimumab biosimilars (the generic equivalents of Humira) are now available in the US and Europe. Several carry an "interchangeable" designation — meaning a pharmacist can substitute them for the original without a new prescription in many places. Ustekinumab biosimilars (equivalents of Stelara) began entering the market in 2025, with six launched in the US by mid-year, significantly reducing costs for this previously expensive treatment. Biosimilars of infliximab (the equivalent of Remicade) have been available for several years with a reassuring real-world safety record. Access still varies depending on your country, health insurer, and what your doctor's pharmacy lists — but the direction of travel is clearly towards greater affordability.
Studies comparing adalimumab biosimilars with the original Humira in psoriasis patients across France, the UK, and Spain found comparable effectiveness and safety over time (drug survival). If you are currently on a biologic and your doctor or insurer suggests switching to a biosimilar, it is worth discussing any questions or concerns with your dermatologist. Individual factors — including how well your current treatment is working and your history with the medication — are all part of that conversation.
Other forms of psoriasis and special populations
Pustular psoriasis
This article focuses on plaque psoriasis, the most common form. Generalised pustular psoriasis (GPP) is a rare and more severe variant where the skin develops widespread fluid-filled bumps (pustules) rather than plaques, often accompanied by fever and systemic illness. It is treated very differently. Spesolimab is a targeted therapy specifically approved for GPP in adults and in young people aged 12 and older — it works by blocking an inflammatory signal called IL-36 (an IL-36 receptor antagonist) that is particularly active in this variant. If you have GPP or suspect you might, it is important to be managed by a dermatologist experienced with this condition.
Paediatric psoriasis
Most of the clinical trial data in this article relates to adults. Psoriasis in children and teenagers follows similar treatment principles but the range of approved medicines is smaller, and dosing is different. The good news is that this is changing. In September 2025, guselkumab became the first IL-23 inhibitor approved for children aged 6 and over weighing at least 40 kg, following a clinical trial (PROTOSTAR) where 56% of paediatric patients achieved 90% skin improvement within 16 weeks — results comparable to adults. If your child has psoriasis, ask for a referral to a dermatologist with experience in paediatric skin conditions.
Beyond medication
Medications, whether topicals, systemics, or biologics, suppress the immune response that drives psoriasis. What they cannot do is address the underlying triggers that repeatedly activate that response. Gut dysbiosis, chronic psychological stress, poor sleep, and sedentary behaviour are well-documented factors associated with the inflammatory state in psoriasis, though their causal role in individual cases varies.
This is not an argument against medication. It is an observation that medication and trigger awareness operate on different aspects of the same disease. Identifying your personal triggers through structured tracking, which is what Itchi is built to help you do, works alongside your treatment plan, not instead of it.
This article is for educational purposes only. It does not constitute medical advice, diagnosis, or treatment recommendation. All medication information is sourced from peer-reviewed literature and clinical guidelines as cited below. Consult your dermatologist or a licensed healthcare professional before making any changes to your treatment plan.
This article was researched and drafted with AI assistance (Claude, Anthropic). All clinical information is sourced from peer-reviewed literature and official guidelines as cited. No clinical claims were generated or fabricated by AI.
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AAD-NPF Joint Guidelines of care for management of psoriasis. American Academy of Dermatology
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Long-term real-world efficacy of methotrexate in psoriasis vulgaris. PMC10869019
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Biologics for moderate-to-severe plaque psoriasis: network meta-analysis. PMC12126413
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WHO Expert Committee on psoriasis treatment landscape 2024. WHO EML 2025
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Deucravacitinib: a novel TYK2 inhibitor for moderate-to-severe psoriasis — efficacy and safety review. PMC10768812
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Adalimumab biosimilars vs originator in psoriasis: multinational cohort study. PubMed 39565180
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FDA approval of guselkumab for paediatric plaque psoriasis and psoriatic arthritis (PROTOSTAR trial). FDA Drug Trials Snapshots — Tremfya, 2025
