Measuring How Much Hair Alopecia Has Taken

What does a SALT score actually measure?

It measures one thing: the share of the scalp that has lost hair, expressed as a percentage from 0 to 100. Nothing else feeds into it — not how long it has been going on, not how fast it moved, not how much it matters to you. SALT stands for Severity of Alopecia Tool, and it was specified in the National Alopecia Areata Foundation's investigational assessment guidelines as the standard way to quantify percentage scalp hair loss 1Ref 1Olsen EA, Hordinsky MK, Price VH, et al. (2004).Alopecia areata investigational assessment guidelines--Part II. National Alopecia Areata Foundation.That the Severity of Alopecia Tool was specified in the National Alopecia Areata Foundation's Part II investigational assessment guidelines as the consensus instrument for quantifying the percentage of scalp hair lost in alopecia areata, and that this document defines the measurement rather than severity bands or change thresholds..

Alopecia areata is an autoimmune disease: the immune system attacks hair follicles, most often producing round patches of loss, and its course is famously unpredictable — hair can return on its own, and it can go again 2Ref 2National Institute of Arthritis and Musculoskeletal and Skin Diseases (2024).Alopecia Areata.The definitional statement that alopecia areata is an autoimmune disease in which the immune system attacks hair follicles, typically causing patchy hair loss, and that its course is unpredictable, with regrowth possible and no cure.. A single number is a crude description of something that moves. It exists because trials needed a common yardstick, and because "a bit worse than last time" is not something two clinicians can agree on across a six-month gap.

How the scalp gets divided into four regions

The scalp is not scored as one surface. It is split into four regions, and each region contributes to the total in proportion to how much of the scalp it represents: the top carries the most weight, the back somewhat less, and the two sides least. Within each region the clinician estimates the percentage of hair missing, multiplies it by that region's share, and sums the four numbers.

The region weights in common use:

That weighting is why two people who both describe "three bare patches" can score very differently. A patch on the crown moves the number more than the same patch above an ear, because there is simply more scalp up there. It is also why the score is meant to be done by someone looking at the whole head, including the back — the part you cannot see and the part that most often gets underestimated.

Where do the severity bands come from?

They come from later research, not from the guideline that defined the tool. The original document specified how to measure percentage scalp hair loss; it did not hand down a table of mild, moderate and severe 1Ref 1Olsen EA, Hordinsky MK, Price VH, et al. (2004).Alopecia areata investigational assessment guidelines--Part II. National Alopecia Areata Foundation.That the Severity of Alopecia Tool was specified in the National Alopecia Areata Foundation's Part II investigational assessment guidelines as the consensus instrument for quantifying the percentage of scalp hair lost in alopecia areata, and that this document defines the measurement rather than severity bands or change thresholds.. The cutoffs people quote — most often 50, meaning half the scalp, as the line into severe — took shape afterwards, in clinical trials and in specialist consensus.

This is not unique to hair. The same layering happens with psoriasis severity, where a validated way to measure the skin came first and the thresholds that decide what gets prescribed were built on top of it later. The practical consequence is the same in both: the measurement is durable, the band is a working convention, and different practices and different insurers may draw the line in slightly different places. Worth asking which threshold your dermatologist's plan is using, and writing the number down — the same score can mean different next steps under different definitions.

What the top of the scale looks like

A score of 100 means no scalp hair at all. When alopecia areata takes the entire scalp it is called alopecia totalis; when it takes the scalp along with brows, lashes and body hair, it is called alopecia universalis. Those are names for extent, not different diseases, and they sit at the ceiling of the same 0-to-100 scale on which a single coin-sized patch is scored.

A ceiling has an awkward property. Once a score is 100, the number stops being able to describe change in either direction. Regrowth over a palm-sized area moves it off 100 and is real progress. Regrowth of eyelashes does not move it at all, because lashes were never in the score to begin with.

What SALT does not count

Everything below the hairline. Eyebrows, eyelashes, beard, body hair and nail pitting are outside the score entirely, which is why someone with a modest scalp number can be having a far harder time than the figure suggests. Alopecia beyond the scalp is assessed, when it is assessed at all, with separate tools that never fold into the single number in the chart.

It also does not count the parts that make this hard: the time in front of a mirror, the wind, whether swimming quietly stopped happening, how it feels to be asked about it at work. A low score is not a verdict that this is a small problem. It is a statement about square centimetres, and the appointment is the place where the rest of it gets said out loud.

How the number enters a treatment decision

Extent is the main lever. Limited, patchy loss is generally approached with treatments applied to or injected into the affected skin; extensive loss is where systemic alopecia treatment — something taken by mouth that acts on immune signalling — comes into the conversation. The phase 3 baricitinib trials that produced the first systemic approval for alopecia areata enrolled adults with severe disease and used the SALT score as their outcome measure 3Ref 3King B, Ohyama M, Kwon O, et al. (2022).Two Phase 3 Trials of Baricitinib for Alopecia Areata.That the phase 3 BRAVE-AA1 and BRAVE-AA2 trials of oral baricitinib enrolled adults with severe alopecia areata and used a SALT score of 20 or less at week 36 as the regrowth endpoint, forming the basis of the first systemic approval in alopecia areata..

Those trials also fixed what "response" means in the literature: a SALT score of 20 or less — at most a fifth of the scalp still bare — assessed at week 36 rather than whenever the hair happened to look best 3Ref 3King B, Ohyama M, Kwon O, et al. (2022).Two Phase 3 Trials of Baricitinib for Alopecia Areata.That the phase 3 BRAVE-AA1 and BRAVE-AA2 trials of oral baricitinib enrolled adults with severe alopecia areata and used a SALT score of 20 or less at week 36 as the regrowth endpoint, forming the basis of the first systemic approval in alopecia areata.. The endpoint is worth knowing for its timescale as much as its threshold. Hair does not answer a question in a fortnight, and a treatment judged at three weeks has not really been judged. Alopecia areata treatment options belong to their own discussion; the point here is that the score is what opens the door to them.

This number does not apply to pattern hair loss

SALT was built for alopecia areata, and it does not describe androgenetic alopecia — the gradual thinning at the crown or the receding front that runs in families. Pattern loss is graded on separate scales that describe shape rather than percentage, and the treatments studied for it are a different set: minoxidil, finasteride and low-level laser therapy have meta-analytic support for promoting growth in men, and minoxidil in women 4Ref 4Adil A, Godwin M (2017).The effectiveness of treatments for androgenetic alopecia: A systematic review and meta-analysis.That minoxidil, finasteride and low-level laser therapy have meta-analytic support for promoting hair growth in men with androgenetic alopecia, and minoxidil in women — a distinct evidence base from alopecia areata..

The distinction matters most at the first appointment, because the two can share one head. Hair-loss treatment evidence diverges sharply between them, and a drug with good trial support for one may have none at all for the other. If a score has been quoted to you, it is fair to ask which condition it was scoring.

Tracking it between appointments

Self-scoring is not the point — SALT is a clinician-rated measure, and a number you assign yourself is a number you can talk yourself out of an appointment with. What travels well is photographs. Four of them, one per region: the top looking down, the back caught in a second mirror or with a phone held overhead, and each side square-on.

• Same light, same time of day, same phone, hair parted the same way.
• Date every set, even the ones that look identical to the last.
• Photograph regrowth as well as loss — early regrowth is often fine and white, and it is easy to miss in a bathroom mirror.
• Keep them in one album, so six months of them can be scrolled in ten seconds.

A dermatologist can read a dated sequence far better than either of you can reconstruct "about the same, maybe slightly worse." It is also the only reliable way to catch the slow direction of travel, which is the thing the eye is worst at seeing in its own reflection.