Is ITA° more accurate than the Fitzpatrick quiz?

It's more objective, an actual measurement rather than recalled behaviour. In research settings with calibrated instruments it's the standard for classifying skin tone. From a phone camera it inherits lighting and camera error, which is why Sunwise treats it as an estimate with a stated confidence rather than a diagnosis.

Does my ITA° change when I tan?

Yes, tanning lowers L* and shifts b*, dropping your angle, and winter fade raises it back. That's a feature: your current tolerance genuinely differs from your untanned baseline, and a live measurement reflects it.

What lighting gives the best photo measurement?

Soft, even, natural daylight, near a window, no direct sun or harsh shadows, no coloured light bouncing in. Sunwise's quality gates reject frames that are too dark, blown out, or don't look like skin, but good light in produces the best estimate out.

Why the inner arm, not my face or belly?

Face and belly tan. Constitutive pigmentation, the baseline ITA° is designed to measure, is read on sun-protected skin. Research uses the buttock or the inner upper arm; the inner arm is the one you can photograph yourself. A tanned belly would make the estimate look more sun-tolerant than you are.

ITA°: the colour angle that measures skin tone

Ask people their skin type and you get memory and self-image. Measure it and you get the Individual Typology Angle, ITA°, dermatology research's standard way of putting a number on skin tone. It's a single angle computed from two colour measurements, and it's how Sunwise turns a photo into a skin-type estimate without asking you a single question.

The formula, in plain language

Colour science describes any colour in the CIELAB space with three values; skin tone mostly lives in two of them: L\* (lightness, 0–100) and b\* (the yellow–blue axis, skin sits on the yellow side). ITA° combines them: **ITA° = arctan((L\* − 50) ÷ b\*) × 180 ÷ π**. Lighter, less-yellow skin produces a high angle; deeply pigmented skin produces a low or negative one. The angle tracks melanin content closely, which is what makes it useful.

The six ITA bands

Bands from dermatology research; Fitzpatrick correspondence is approximate by design.
ITA° range	Category	≈ Fitzpatrick type
> 55°	Very light	I
41° – 55°	Light	II
28° – 41°	Intermediate	III
10° – 28°	Tan	IV
−30° – 10°	Brown	V
≤ −30°	Dark	VI

Why measure instead of ask?

Because self-report drifts. Studies comparing questionnaires with measured ITA° find people routinely misplace themselves, and the Fitzpatrick questionnaire's burn/tan framing works worst for darker skin, where 'do you burn?' was never a well-designed question. ITA° doesn't care what you remember about last summer. It also captures something a lifetime label can't: your skin as it is right now, including your current tan, which is the relevant input for today's sun decisions.

Where to photograph

ITA° is meant to capture constitutive pigmentation, the baseline melanin you have without a tan. In the lab that is measured on skin that rarely sees the sun. The gold-standard site is the buttock; colourimetry studies also use the medial inner upper arm, close to the armpit, because it tracks buttock readings closely, stays relatively untanned, and people will actually let you measure it. The belly, face and outer arms are facultative sites: they tan, which shifts ITA° and can make a photo check read darker (and therefore less sun-sensitive) than your true baseline.

Sunwise asks for the inner upper arm because it is the research site that is also easy to photograph on a phone: roll up a sleeve, hold the inside of your upper arm about 30 cm from the camera, and keep the centre square on untanned skin. Skip moles, tattoos and the armpit fold itself.

How Sunwise uses it, and its honest limits

The photo check samples a 30×30 pixel patch from the inner-arm skin in the frame's centre, filters out non-skin pixels, converts the median tone to CIELAB, computes ITA°, and maps the angle to an approximate Fitzpatrick type and its typical burn threshold. Photos are analysed in memory and discarded. The limits are real and worth stating: consumer cameras auto-correct colour, lighting shifts L\* and b\*, and a phone photo is not a calibrated colorimeter. Sunwise scores capture quality and reports its confidence, treat the result as a good estimate, and every burn time as a ceiling to stay well under.

Frequently asked questions

Is ITA° more accurate than the Fitzpatrick quiz?: It's more objective, an actual measurement rather than recalled behaviour. In research settings with calibrated instruments it's the standard for classifying skin tone. From a phone camera it inherits lighting and camera error, which is why Sunwise treats it as an estimate with a stated confidence rather than a diagnosis.
Does my ITA° change when I tan?: Yes, tanning lowers L* and shifts b*, dropping your angle, and winter fade raises it back. That's a feature: your current tolerance genuinely differs from your untanned baseline, and a live measurement reflects it.
What lighting gives the best photo measurement?: Soft, even, natural daylight, near a window, no direct sun or harsh shadows, no coloured light bouncing in. Sunwise's quality gates reject frames that are too dark, blown out, or don't look like skin, but good light in produces the best estimate out.
Why the inner arm, not my face or belly?: Face and belly tan. Constitutive pigmentation, the baseline ITA° is designed to measure, is read on sun-protected skin. Research uses the buttock or the inner upper arm; the inner arm is the one you can photograph yourself. A tanned belly would make the estimate look more sun-tolerant than you are.

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