When a dermatologist calls psoriasis "mild," "moderate" or "severe," that's not a guess — it comes from measurable scores. Three in particular do most of the work: BSA, PASI and DLQI. Here's what each one measures, what counts as severe, and how they guide treatment.
Dermatologists grade psoriasis severity with a mix of scores: BSA (how much skin is affected), PASI (a single number blending area with redness, thickness and scaling, from 0 to 72), and DLQI (how much it affects daily life, from 0 to 30). A handy shortcut, the "rule of tens", calls psoriasis severe if BSA >10%, PASI >10, or DLQI >10 — which often prompts stronger treatment. No single number tells the whole story.
Psoriasis severity is measured with three main scores, usually together. BSA (Body Surface Area) is the percentage of skin affected — one handprint ≈ 1% of the body; over ~10% is severe. PASI (Psoriasis Area and Severity Index) combines the area involved with the redness, thickness and scaling of plaques into a single number from 0 to 72 (broadly, under ~5 mild, ~5–10 moderate, over 10 severe — cut-offs vary). DLQI (Dermatology Life Quality Index) is a 10-question survey scoring the impact on daily life from 0 to 30. The "rule of tens" flags severe disease if any of BSA, PASI or DLQI exceeds 10 — a common trigger to consider systemic or biologic treatment. These are your dermatologist's tools to choose and track therapy.
Why Measure Psoriasis Severity?
Grading severity isn't box-ticking — it does three practical jobs. It classifies psoriasis as mild, moderate or severe; it guides treatment choice (topicals for milder disease; phototherapy, systemic medicines or biologics as severity rises); and it tracks response over time, so a dermatologist can see whether a treatment is working and adjust it.
To do that well, the scores capture different angles — how much skin is involved, how intense the plaques are, and how much psoriasis is affecting the person's life. That's why more than one is used.
BSA — How Much Skin Is Affected
The Body Surface Area (BSA) score is the simplest: it estimates the percentage of skin covered by psoriasis. A convenient rule of thumb is that one handprint — palm plus fingers — is roughly 1% of your body, so a clinician can "count handprints" to gauge extent. Broadly, under about 3% is mild, 3–10% moderate, and over 10% severe.
Its weakness: BSA ignores location and impact. A small amount of psoriasis on the hands, face or genitals can be far more distressing and disabling than a larger patch on the back — so BSA alone can understate how much psoriasis really matters to someone.
PASI — The Clinical Gold Standard
The Psoriasis Area and Severity Index (PASI) is the most widely used measure. It blends the area affected with three plaque qualities — redness (erythema), thickness (induration) and scaling (desquamation) — each rated across four body regions (head, trunk, arms and legs), which are weighted by their share of body surface. The result is a single number from 0 (no psoriasis) to 72 (most severe).
As a rough guide, a PASI under about 5 is mild, roughly 5–10 moderate, and above 10 severe — though exact cut-offs differ between guidelines, and a PASI over 10 is a common threshold for considering stronger (systemic or biologic) treatment.
PASI also tracks improvement: you'll see PASI 75, 90 and 100 — meaning a 75%, 90% or 100% reduction from the starting score. PASI 75 was the long-standing benchmark for a treatment "working"; with newer biologics, near-clear (PASI 90) or clear (PASI 100) skin is increasingly the goal. Its limitations: it's complex to score, less sensitive at the mild end, doesn't capture nail, scalp or genital psoriasis well, and says nothing about quality of life — which is exactly why DLQI is used alongside it.
DLQI — The Quality-Of-Life Picture
Skin scores don't capture how psoriasis feels to live with — the Dermatology Life Quality Index (DLQI) does. It's a short patient questionnaire: ten questions, each scored 0 to 3, for a total of 0 to 30, asking how much your skin has affected the past week — work or study, relationships, daily activities, choice of clothing, and even the hassle of treatment. A higher score means a bigger impact.
This is where a "small" case can reveal its true weight: psoriasis on visible or sensitive areas can score high on DLQI even with a low BSA — capturing the human burden the skin measures miss.
Putting Them Together: The "Rule Of Tens"
Because each score sees only part of the picture, they're used together. A widely quoted shortcut is the "rule of tens": psoriasis is considered severe if BSA > 10%, or PASI > 10, or DLQI > 10. Meeting any one of these often prompts a dermatologist to consider systemic or biologic therapy rather than topicals alone.
Clinicians may also use a quick global rating — the Investigator's (or Physician's) Global Assessment (IGA/PGA), a simple "clear" to "very severe" scale — as an at-a-glance summary. The theme throughout: severity is extent, intensity and life-impact together, not one number in isolation.
What This Means For You
If your dermatologist mentions a PASI or DLQI, these are simply the tools they use to tailor and track your treatment — a shared, objective language for "is this getting better?" They're also a useful reminder that severity isn't only skin-deep: how much psoriasis affects your sleep, confidence and daily life genuinely counts, and it's worth telling your doctor if it's weighing on you. A score is a snapshot to guide care — it doesn't define you, and psoriasis is very manageable with the right plan. It also helps to understand what drives psoriasis and how factors like stress can influence flares — and to remember that measures like PASI can under-count areas such as the nails, so tell your dermatologist about symptoms the score might miss.
- Three main scores — BSA (extent), PASI (extent + intensity), DLQI (life-impact).
- PASI runs 0–72 — above ~10 is commonly severe; cut-offs vary.
- BSA: handprint ≈ 1% — over 10% is severe; but it ignores location.
- DLQI runs 0–30 — a patient survey of daily-life impact.
- Rule of tens — any of BSA/PASI/DLQI over 10 flags severe disease.
Psoriasis severity is assessed with three complementary scores: BSA (how much skin), PASI (extent plus redness, thickness and scaling, 0–72), and DLQI (life-impact, 0–30). The "rule of tens" — any of them over 10 — is a quick flag for severe disease and often the cue to step up treatment, while PASI 75/90/100 track how well therapy is working. They're your dermatologist's tools to guide care — and a reminder that psoriasis severity is about your life, not just your skin.
We like that psoriasis scoring bakes in quality of life, not just square-centimetres of skin — because the DLQI is often where a "small" case shows its real weight. If you're tracking your own psoriasis, the practical takeaway is simple: note not just where and how bad the plaques are, but how much they're affecting your days, and bring that to your dermatologist. The numbers exist to get you the right treatment faster — they're a compass, not a verdict.
Frequently Asked Questions
How is the severity of psoriasis assessed?
Dermatologists use a combination of scores. BSA (Body Surface Area) measures how much skin is affected; PASI (Psoriasis Area and Severity Index) combines how much skin is involved with how red, thick and scaly the plaques are into a single number; and DLQI (Dermatology Life Quality Index) captures how much psoriasis affects daily life. Used together, they classify psoriasis as mild, moderate or severe and guide treatment.
What is a PASI score, and what counts as severe?
PASI (Psoriasis Area and Severity Index) runs from 0 (no psoriasis) to 72 (most severe). It blends the area affected with the redness, thickness and scaling of plaques across four body regions. Broadly, under about 5 is mild, roughly 5–10 moderate, and above 10 severe — though exact cut-offs vary between guidelines, and a PASI above 10 is a common threshold for considering stronger (systemic or biologic) treatment. PASI is also used to track improvement, as PASI 75/90/100.
What is BSA in psoriasis?
BSA (Body Surface Area) is the percentage of skin covered by psoriasis. A handy rule is that one handprint (palm and fingers) is roughly 1% of the body. Broadly, under about 3% is mild, 3–10% moderate, and over 10% severe. Its limitation is that it doesn't account for where the psoriasis is — a small amount on the hands, face or genitals can affect life far more than a larger patch on the back.
What is the DLQI?
The DLQI (Dermatology Life Quality Index) is a short patient questionnaire — ten questions, each scored 0 to 3, for a total of 0 to 30 — about how much a skin condition has affected daily life over the past week, from work and relationships to clothing and treatment. A higher score means a bigger impact. It captures the human burden of psoriasis that the skin-based scores can miss.
What is the "rule of tens" in psoriasis?
The "rule of tens" is a quick way to flag severe psoriasis: it's considered severe if BSA is over 10%, or PASI is over 10, or DLQI is over 10. Meeting any one of these often prompts a dermatologist to consider stronger treatment, such as systemic or biologic therapy. It's a reminder that severity is about extent, intensity and life-impact together — not one number alone.
Boldpurity Science Team
Boldpurity is a clinical skincare brand with in-house cGMP manufacturing in Hyderabad, India, formulating evidence-led skincare for medium-to-deep skin tones. Content is prepared and science-reviewed by the Boldpurity Science Team.
Editorial Process
Articles are drafted from peer-reviewed dermatology literature and authoritative clinical sources, science-reviewed for accuracy, and kept at an education level. We report severity thresholds honestly (noting where cut-offs vary), make no product claims, and frame scoring as a clinician's tool.
Reference Policy
Claims are supported by cited sources (see References), including dermatology guidance on the PASI, BSA and DLQI. Score ranges and cut-offs are presented as general guides, since conventions vary between guidelines.
Medical Disclaimer
This article is general information, not medical advice, and does not diagnose or treat any condition. Severity scoring and treatment decisions should be made by a doctor or dermatologist. If psoriasis is affecting your skin or your quality of life, seek professional assessment.
This article is educational, does not diagnose or treat any condition, and does not recommend specific products. Severity scores (PASI, BSA, DLQI) and their thresholds are general guides that vary between clinical guidelines; scoring and treatment decisions are made by a doctor or dermatologist. Consult a dermatologist for assessment and management of psoriasis.
- American Academy of Dermatology (AAD). Psoriasis: diagnosis and treatment. aad.org.
- DermNet. Psoriasis Area and Severity Index (PASI). dermnetnz.org.
- Fredriksson T, Pettersson U. Severe psoriasis — oral therapy with a new retinoid. Dermatologica. 1978.
- Liluashvili S, et al. Dermatology Life Quality Index and disease coping strategies in psoriasis patients. Postepy Dermatol Alergol. 2019.
