How do dermatologists put a number on psoriasis?
Usually with a percentage and a rating. The percentage is body surface area, the share of your skin psoriasis covers. The rating is a global assessment, where a clinician grades your skin on a short scale. Evidence Evidence Evidence
Why this matters
- Sources cited, not yet graded
I read the International Psoriasis Council, and it uses both. It puts one line at 10 per cent of the body surface. It pairs that with a physician global assessment. It defines clear or almost clear skin as 1 per cent or less body surface, with an assessment of 0 or 1. The National Psoriasis Foundation records that moderate-to-severe psoriasis is not decided by body surface area alone. NICE assesses the skin, the nails, high-impact sites, the effect on daily life and any joint concerns.
Considerations
- Depends on you
A percentage is an estimate, not a measurement. I looked for the handprint shorthand you may have been told, where one handprint stands for about 1 per cent of your skin. None of these sources publishes it. I compared the two wordings IPC gives for its own threshold in its June 2025 deck. The summary says 10 per cent or more. The slide below it says above 10 per cent. NICE is UK guidance and sets no US coverage rule.
Questions for your dermatologist
What is my body surface area today, and how did you work it out?
Saving keeps this on your device and needs JavaScript, which is off in this browser.Does one of my handprints count as about 1 per cent when you estimate it?
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What is PASI, and what does it score?
PASI is the Psoriasis Area and Severity Index. Fredriksson and Pettersson described it in 1978. It grades three things about your skin, then sets them against how much skin is involved. Evidence
Why this matters
- Sources cited, not yet graded
The three are redness, thickness and scale. Each is graded from 0 to 4. Area is graded separately, from 0 to 6. The body is split into four regions: the head, the upper limbs, the trunk and the lower limbs. Each region carries its own weight, because each holds a different share of your skin. The four region scores are added. The total runs from 0 to 72, and a higher number means more. Trial reports use it constantly, which is where PASI 75 and PASI 90 come from.
Considerations
- Depends on you
I went through the 1978 paper for how closely two clinicians scoring the same skin agree, and it does not report that. It does not say how the redness grade behaves on brown or black skin. It sets no score at which a person qualifies for anything. I could not find which health plans ask for a PASI number, in that paper or in the other sources here.
Questions for your dermatologist
Do you score my psoriasis with PASI, or with something else?
Saving keeps this on your device and needs JavaScript, which is off in this browser.Which number of mine would go on a prior authorization form?
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Does the effect on your life count?
Yes, and it is measured too. The Dermatology Life Quality Index is the usual form for it. Finlay and Khan described it in 1994, and it takes a couple of minutes. Evidence Evidence Evidence
Why this matters
- Sources cited, not yet graded
I read the form itself. It asks ten questions, and every one is about the last seven days. They cover symptoms and feelings, daily activities, leisure, work or study, personal relationships, and the trouble of the treatment itself. Each answer scores 0 to 3, so the total runs from 0 to 30. A higher total means a heavier effect. NICE puts the effect on daily life inside the assessment, beside the skin and the nails. NIAMS records that psoriasis carries risk for low self-esteem, anxiety and depression.
Considerations
- Depends on you
The 1994 paper I read is a first validation of a questionnaire, not a study of treatment. It sets no score at which a person qualifies for anything. A form about one week cannot see a better week or a worse one. Your worst week may be the one you are not asked about.
Questions for your dermatologist
Can we fill in a quality-of-life form together and keep it in my notes?
Saving keeps this on your device and needs JavaScript, which is off in this browser.Which parts of my week do you want me to write down before my next visit?
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Why does the number matter for what a plan covers?
Because a plan often reads one number and stops there. Two bodies have said that one number is not the whole picture, and I read both statements in writing you can point to. Evidence Evidence
Why this matters
- Sources cited, not yet graded
Whether you can afford a treatment, and what prior authorization involves, is one of the questions psoriasis readers ask most. The International Psoriasis Council dropped the mild, moderate and severe scale. In its place a person is a candidate for topical therapy, or a candidate for systemic therapy. Any one of three criteria is enough for the second group. The first is 10 per cent or more of the body surface. The second is a high-impact site, and IPC names the face, palms, soles, genitalia, scalp and nails. The third is failure of topical therapy, defined as not reaching clear or almost clear skin after two four-week courses in a row. The National Psoriasis Foundation said the same thing in its 2025 position statement, and named the genitals, hands, feet, face, scalp and nails.
Considerations
- Depends on you
Neither body sets a health plan rule. IPC is a professional consensus and NPF is an advocacy organization, and I checked their member pages: both name drug makers among their corporate members. I could not find a prior authorization step, an appeal route or a deadline in either statement. Neither says how much topical treatment counts as inadequate control, or over what period.
Questions for your dermatologist
Which of the three criteria do I meet, and will you write that in my notes?
Saving keeps this on your device and needs JavaScript, which is off in this browser.If my percentage is small, will the site and the effect on my week be recorded as well?
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How do you bring your own estimate to a visit?
Write it down before you go, and take pictures. The National Psoriasis Foundation says to bring a symptom record, on paper or on a phone, and to share it at the appointment. Evidence Evidence Evidence
Why this matters
- Sources cited, not yet graded
I read the foundation page for what it actually asks of you. It says to describe symptoms clearly, and to note changes in severity and in the areas affected. Its flare guide offers a worksheet for daily symptoms and their severity, and says tracking over time helps you work out your own triggers. For photographs, a series that can be compared needs a plain background and a level camera. Use the same light in the same position. Keep the same distance, about three to five feet, and shoot the same body areas every time. Put the date on each picture.
Considerations
- Depends on you
I took the photo method above from a page written for vitiligo, a different condition, and carried over only the camera technique. Neither NPF page gives a percentage or a timeline for what tracking changes. What you bring is a record, not a diagnosis, and it does not set your score. The person who examines your skin does that.
Questions for your dermatologist
Which areas do you want photographed before my next visit?
Saving keeps this on your device and needs JavaScript, which is off in this browser.What would you want to see from me to judge whether this is better or worse?
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Evidence and update context
This optional layer shows the evidence boundary I reviewed as of 2026-09-19.
- What this evidence supports
- I read the International Psoriasis Council, and it uses both. It puts one line at 10 per cent of the body surface. It pairs that with a physician global assessment. It defines clear or almost clear skin as 1 per cent or less body surface, with an assessment of 0 or 1. The National Psoriasis Foundation records that moderate-to-severe psoriasis is not decided by body surface area alone. NICE assesses the skin, the nails, high-impact sites, the effect on daily life and any joint concerns.
- What it does not establish
- A percentage is an estimate, not a measurement. I looked for the handprint shorthand you may have been told, where one handprint stands for about 1 per cent of your skin. None of these sources publishes it. I compared the two wordings IPC gives for its own threshold in its June 2025 deck. The summary says 10 per cent or more. The slide below it says above 10 per cent. NICE is UK guidance and sets no US coverage rule.
Evidence behind this page
Sources
Each evidence badge opens the source and its limits. The full list stays available here.
- National Institute of Arthritis and Musculoskeletal and Skin DiseasesPatient education · Patient education, tier 5Independent source
- Published
- SteadySkin last checked
What this source can and cannot tell you
What this source supports
Supports that poor sleep quality is a listed symptom of psoriasis. Also lists patches of thick, red, scaly skin that itch or burn, and dry, cracked skin that itches or bleeds. Supports that psoriasis carries risk for mental-health concerns including low self-esteem, anxiety, and depression. Supports that managing common triggers, such as stress and skin injuries, can help keep symptoms under control. Supports, by subtype, that guttate psoriasis outbreaks are often triggered by an upper respiratory infection such as strep throat. Also supports that pustular psoriasis symptoms can be triggered by medications, infections, stress, or certain chemicals. Also supports that erythrodermic psoriasis can be triggered by a bad sunburn or certain medications including corticosteroids. Also supports, by subtype, that inverse psoriasis appears as smooth patches of inflamed skin in skin folds. It names the armpits, the groin, and under the breasts as those folds. It records that rubbing and sweating can make inverse psoriasis worse.
What it does not support
Does not give a percentage of patients affected. Does not measure how much sleep is lost. Does not establish that treating the skin fixes the sleep problem for any one person. Its trigger information is organized by psoriasis subtype, not as one general list for plaque psoriasis specifically. It counts nothing for inverse psoriasis either. It gives no share of people affected in a fold or genital site, and it names no treatment for one.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- International Psoriasis CouncilGuideline · Clinical research, tier 2Relevant relationship disclosed
- Published
- SteadySkin last checked
What this source can and cannot tell you
Why the independence label says this: The International Psoriasis Council names its corporate members on its own site (psoriasiscouncil.org/about/corporate-members/, checked 2026-09-11). The top tier names AbbVie, Johnson & Johnson, Eli Lilly, Novartis and Takeda. LEO Pharma, UCB, Almirall, Sun Pharma, Amgen, Alumis, Arcutis and Oruka sit below them. Those firms make the drugs this severity rule opens the door to. A wider rule on who qualifies is a wider market for them. The page says nothing about how that money relates to IPC independence.
What this source supports
Supports that IPC dropped the mild, moderate and severe scale. In its place a person is a candidate for topical therapy, or a candidate for systemic therapy. Supports that any one of three criteria is enough to be a candidate for systemic therapy. The first is psoriasis on 10% or more of the body surface. The second is psoriasis on a high-impact site. IPC names those sites as the face, palms, soles, genitalia, scalp and nails. The third is failure of topical therapy. Supports that IPC defines that failure in writing. It is not reaching clear or almost-clear skin after two four-week courses in a row. IPC gives clear or almost-clear as 1% or less body surface, with a physician global assessment of 0 or 1. Supports the source paper. It is Strober B, Ryan C, van de Kerkhof P, et al. Recategorization of psoriasis severity: Delphi consensus from the International Psoriasis Council. J Am Acad Dermatol 2020 Jan;82(1):117-122. Supports that IPC's own June 2025 teaching deck lists payers among the groups it set out to move. That deck also names refusal to pay as a result of the older scale.
What it does not support
Does not set any health plan's coverage rule. This is a professional-society consensus. It is not a regulation and not a plan document. Does not say which systemic treatment follows once a person meets a criterion. It sets no dose, no frequency and no schedule. Does not give the number of experts who voted, the response rate, or their conflict-of-interest disclosures. IPC's own June 2025 deck states the body-surface threshold two ways. Its criteria summary says 10% or more. The slide expanding that criterion says above 10%. Does not establish that a given reader meets a criterion. It predicts nothing about what a plan will decide.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- National Psoriasis FoundationPatient education · Patient education, tier 5Relevant relationship disclosed
- Published
- SteadySkin last checked
What this source can and cannot tell you
Why the independence label says this: The National Psoriasis Foundation names its corporate members on its own site (psoriasis.org/corporate-members/, checked 2026-09-09). They include AbbVie, Johnson & Johnson, Leo Pharma, Lilly, Novartis, UCB, Amgen, Sun Pharma, Arcutis, Bristol Myers Squibb, Takeda, and Alumis. Several of those firms make the drugs step therapy and copay-card rules affect. NPF also lobbies against both practices. This number and its framing come from a group with a stake in the fight, even though NPF says it does not back one drug over another.
What this source supports
Supports that NPF adopted a two-class definition. Mild psoriasis can be managed with topical therapies. Moderate-to-severe psoriasis makes a person a candidate for advanced therapies. Supports its statement that "Moderate-to-severe psoriasis is not determined solely by body surface area (BSA) involvement of 10%." Supports that psoriasis on a high-impact site counts too. NPF gives those sites as the face, scalp, hands, feet, nails or genitals. It says such patients "should also be considered as having 'moderate-to-severe' disease". Supports that the same holds for people who cannot get adequate control from topical therapies. Supports its statement that "People with psoriasis should never be denied advanced care because of outdated measures."
What it does not support
Does not set any health plan's coverage rule and does not bind a payer. Does not name prior authorization, appeals or denial steps. Gives no appeal deadline and no appeal process. Does not say how much topical treatment counts as inadequate control, or over what period. Does not establish that a given reader is a candidate for a named therapy. It predicts nothing about what a plan will decide.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- National Psoriasis FoundationPatient education · Patient education, tier 5Independent source
- Published
- SteadySkin last checked
What this source can and cannot tell you
What this source supports
Supports that tracking symptoms and common triggers over time can help a person figure out their own specific triggers. Supports naming stress, alcohol, and diet as examples of common triggers to watch for. Supports naming discolored skin patches and itching as psoriasis symptoms, and joint swelling and fatigue as psoriatic arthritis symptoms, to watch for. Supports using a worksheet to record daily symptoms and their severity, and sharing that worksheet with a health care provider.
What it does not support
Does not give a percentage or timeline for how much tracking changes any one outcome. Does not name every possible trigger - stress, alcohol, and diet are examples, not a complete list. Does not measure whether tracking itself helps or burdens a given person.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- National Psoriasis FoundationPatient education · Patient education, tier 5Independent source
- Published
- SteadySkin last checked
What this source can and cannot tell you
What this source supports
Supports bringing a symptom tracker, kept on paper or on a phone, to share with a doctor at an appointment. Supports clearly describing symptoms and noting changes in severity and affected areas as part of preparing for a visit.
What it does not support
Does not mention photographing skin changes specifically. The page shows no visible byline or update date. The site copyright year, 2026, is used here.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- MyVitiligoTeamPatient education · Patient education, tier 5Independent source
- Published
- SteadySkin last checked
What this source can and cannot tell you
What this source supports
Supports a solid-colored background for a comparable photo series. Black, green, or dark blue are named as ones that help skin stand out. Supports using the same artificial light in the same position each time, rather than sunlight. Supports holding the camera straight rather than tilted. Supports a distance of about 3 to 5 feet, held the same every time. Supports photographing a fixed list of body areas the same way every time. Supports using a ruler for scale and tagging each photo with its date.
What it does not support
Written and reviewed for tracking vitiligo, a different condition, not for psoriasis. Only the general camera technique - background, lighting, angle, distance, and framing - is used here; nothing about vitiligo itself is carried over. Does not establish that photo tracking changes any psoriasis outcome.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- Dermatologica 1978;157(4):238-244 (Fredriksson T, Pettersson U)Observational study · Supporting research, tier 3Independence not established
- Published
- SteadySkin last checked
What this source can and cannot tell you
Why the independence label says this: This 1978 paper is the first description of the Psoriasis Area and Severity Index. It is not open access. Any funding or competing-interest statement could not be read, and the study itself tested a drug.
What this source supports
Supports that the Psoriasis Area and Severity Index was first described here. Supports that the index scores three features of the skin: redness, thickness and scale. Supports that each of the three is graded on a scale of 0 to 4. Supports that the amount of skin involved is graded separately, on a scale of 0 to 6. Supports that the body is divided into four regions: the head, the upper limbs, the trunk and the lower limbs. Supports that each region carries its own weight, because each holds a different share of the skin. Supports that the four region scores are added, and that the total runs from 0 to 72.
What it does not support
Does not report how closely two clinicians scoring the same skin agree. Does not say how the redness grade behaves on brown or black skin. Does not set a score at which a person qualifies for any treatment. Does not say which health plans ask for the score. Does not diagnose a reader or predict what one person will score.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- Clinical and Experimental Dermatology 1994;19(3):210-216 (Finlay AY, Khan GK)Observational study · Supporting research, tier 3Independence not established
- Published
- SteadySkin last checked
What this source can and cannot tell you
Why the independence label says this: This 1994 paper is the first description of the Dermatology Life Quality Index. It is not open access, so any funding or competing-interest statement could not be read.
What this source supports
Supports that the Dermatology Life Quality Index was first described here. Supports that it is a ten-question form a person fills in themselves. Supports that every question asks about the last seven days. Supports that it was designed to be quick, and to be used in a routine clinic. Supports that the questions cover symptoms and feelings, daily activities, leisure, work or study, personal relationships, and the trouble of the treatment itself. Supports that each answer scores 0 to 3, and that the total runs from 0 to 30. Supports that a higher total means a heavier effect on life.
What it does not support
Is a first validation of a questionnaire, not a study of psoriasis treatment. Does not set a score at which a person qualifies for any treatment. Does not say which health plans ask for the score. A form about one week does not capture a better or worse week. Does not diagnose a reader or predict what one person will score.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.
- National Institute for Health and Care ExcellenceGuideline · Regulatory / guideline, tier 1Independent source
- Published
- SteadySkin last checked
What this source can and cannot tell you
What this source supports
Supports psoriasis assessment across skin, nails, high-impact sites, life impact and joint concerns; same-day specialist assessment for generalised pustular psoriasis or erythroderma; and a treatment map that includes topical, phototherapy and systemic options.
What it does not support
It is UK guidance and does not diagnose a reader, create a US treatment sequence, determine personal urgency from a description, or establish current US labeling or coverage.
Claim-specific review for this source is still in progress. Only the source-level evidence and limits are shown here.