Two comparable photos

You put two photos of the top of your head side by side, taken three months apart. In the first, under the bathroom light, your parting looks narrow. In the second, taken in sunlight by the window, you can see scalp everywhere. Have you lost hair, or has only the light changed?

There’s no way to tell. For two photos to be comparable, only one thing should have changed between them: your hair. That’s exactly what dermatologists aim for when they photograph hair loss.

Why two photos can lie

The European guideline on androgenetic alopecia ranked the methods for following hair loss. Standardised photos of the whole scalp came out on top, and the authors advise using them in everyday practice too, for long-term follow-up¹. The French Society of Dermatology calls them an excellent monitoring tool, provided they’re taken in a reproducible position⁷.

The reason is simple. Comparing one photo with another is more reliable than remembering what your hair looked like months or years ago². And the eye needs a clear difference to notice anything: in a study cited by a team at Ohio State University, a 22.66% reduction in hair on standardised photos was needed for 75% of dermatologists to detect the change³. If the light or the angle also changes from one photo to the next, the real difference gets lost in the noise.

Flash is a well-known trap. On a hair loss forum, one member describes photographing the crown of a friend with a full head of hair: in the photos, he looked as if he was thinning⁴.

Testimonials posted on the HairLossTalk forum⁴.

What dermatologists do

In specialist clinics, the patient rests their chin and forehead on a fixed device with the camera and flash mounted on it. That way, the view, the magnification and the lighting stay the same from one visit to the next². Staff also try to recreate the same parting and combing as in the first photo².

Dermatologists in India have shown you can get close with very little: a wooden box with a groove for the chin, one for the nose and an edge for the forehead, a background against the wall, a tripod and a chair placed on floor markings⁶. Their principle fits in one sentence: between two photos, everything must stay constant except the state of the hair, from the background and the combing to the head position, the lighting and the camera settings⁶. It’s a short letter describing their tool, with no measurement of how reliable it is.

Having the right equipment isn’t enough. In a dermatology department in Ohio, the team checked the records of patients who came in for hair loss³.

The limits are those of a single department and 50 records per period, and the study doesn’t say whether the improvement lasted³. But the message is clear: taking a comparable photo is something you learn.

The light

British medical photographers use studio flash and a neutral background. They watch for reflections on the skin and move the flash to reduce them⁵.

At home, the idea is the same: one light source, always the same one. Pick a room and a light you’ll find again every week, such as the bathroom ceiling light in the evening, rather than a window whose light changes with the time of day and the season. And decide once and for all: flash or no flash, but the same for every photo. A plain background behind your head helps you see the outline of your hair.

Angle and distance

Medical photographers fix the distance between the camera and the head to avoid perspective distortion, and keep the lens square to the area being photographed⁵. For the crown, they centre the whorl of hair in the frame. For the hairline, they ask the patient to dip their chin and keep the eyebrows in the frame as a reference point⁵.

On a phone, a couple of centimetres closer or a slight tilt is enough to change what you see. Keep fixed reference points: the same position, sitting or standing, the phone held the same way, one point on your face (your eyebrows, the tip of your nose) always in the same spot on the screen. The British guide advises having previous photos to hand during the session to recreate the same positioning⁵. You can do the same.

Your hair on the day

This is the part people forget most. The same guide asks you not to use styling products on the day of the photo and not to wash your hair in the 48 hours before: freshly washed hair is softer and harder to position⁵. It also asks you to be photographed at a similar point in your colouring cycle, for example within a week of dyeing⁵.

Dermatologists ask patients to keep the same hairstyle and colour from one visit to the next². For the parting, the British guide uses the bridge of the nose as the starting point and traces a straight line back to the nape⁵.

In practice, at home:

• hair dry, never wet;
• the same number of days after washing, which matters if you wash your hair often;
• the same parting, in the same place, drawn with a comb;
• no gel, wax or hairspray that day;
• a recent haircut noted somewhere, to explain a difference between two photos.

Which zones to photograph

For male pattern hair loss, the British protocol takes four views: the hairline seen from above, both sides and the crown. For female pattern hair loss, it adds the centre parting seen from above and from behind⁵. The Ohio department required at least three views: the front, the temples and the crown³.

Choose the zones that apply to you. Temples and crown for early male pattern baldness, the parting for hair loss in women, and the back of the head as a benchmark, since it rarely changes. As for frequency, Swiss trichologists recommend a photo review at 3, 6 and 12 months⁸; one photo a week, always the same, lets you see the trend in between. And start before you begin anything: without a starting photo, you have nothing to compare.

Calvap’s ghost photo

Calvap takes these rules and builds them into your camera. At each session, your last photo of the zone shows as a ghost, see-through over the live image. You move the phone until your head lines up with the previous photo, then you shoot: same angle, same distance, no ruler or tripod. Your screen does the job of the dermatologist’s chin rest.

Guided sessions go through the same zones in the same order, from 1 to 7 depending on what you track: hairline, temples, crown, sides, back. The flash is set as it was last time. At the end of the session, two questions record what could explain a difference: hair dry or wet, recent haircut. Photos you import from your gallery are kept apart, as reference points, because they weren’t taken in these conditions.

Your photos are arranged zone by zone on a timeline, alongside your routine. After a few weeks, you drag the slider between your starting photo and today’s, and you see what has moved. They stay on your phone, ready to show your dermatologist. Whether you should count your hairs or photograph them is something we cover separately.