Laser hair removal and the sun: what actually matters

The principle is called selective photothermolysis, and it is elegant. A wavelength of light is chosen because a particular structure absorbs it strongly while the tissue around it does not. The absorbed light becomes heat, and the heat damages that structure while sparing its surroundings.

In hair removal the absorbing structure is melanin, the pigment that gives hair its colour. Light is absorbed along the pigmented shaft, heat travels down to the follicle, and the structures responsible for producing new hair are damaged. The hair itself is only the delivery route.

The difficulty is that melanin is also what colours skin. The laser cannot tell the difference between pigment in a follicle and pigment in the epidermis it has to pass through. The more pigment sitting in the skin, the more energy is absorbed on the way and the narrower the margin between treating the follicle and injuring the surface.

This is not a reason to avoid treatment. It is the reason device choice and settings matter, and why a course that suits one person is not simply copied onto another. Longer wavelengths penetrate more deeply and interact less with surface pigment, which is why they are generally preferred for richly pigmented skin. The assessment before a first session exists to make that judgment.

The risks when the balance is wrong are burns, blistering, and changes in skin colour in the treated area, either darker or lighter. Pigment changes in particular tend to be more persistent in darker skin, which is precisely the population this city mostly serves.

A tan is not a cosmetic state. It is the skin actively producing extra melanin as a protective response to ultraviolet light. From the laser's point of view, a tanned patient is a patient whose epidermis has temporarily become a much stronger competitor for the light.

That extra pigment settles over weeks, not days, which is why clinics ask for a gap after meaningful sun exposure and again before the next session. In practice this is the single most common reason a session is postponed at the door, and postponing is the correct decision rather than an inconvenience.

Self-tanning products count, because they deposit colour in the outer skin layer that the laser will also encounter. So do some skin treatments and products used in the days before a session. Say what you have used rather than assuming it is irrelevant.

Since the treatment depends on pigment in the hair, hair with little pigment gives the laser almost nothing to work with. Grey and white hair, and to a large extent very fine blonde and red hair, respond poorly regardless of the device or the operator. Dark, coarse hair on lighter skin is the easiest combination; dark hair on darker skin is entirely treatable with the right device and appropriate settings.

An honest consultation says this before a course is sold, not after it disappoints. If a large proportion of the hair in an area is grey, expectations should be set accordingly.

Hair does not grow continuously. Each follicle cycles through an active growing phase, a brief transitional phase and a resting phase, and follicles in the same patch of skin are not synchronised. At any given moment only a proportion of them are actively growing.

Only actively growing follicles are meaningfully connected to the structures the treatment targets, so only those respond. The rest are untouched, emerge later, and need their own session. This is why a course is spaced out over months and why the third session is not evidence that the first two failed.

It is also why the honest term is hair reduction rather than removal. Most people see a substantial, lasting decrease in the amount and coarseness of hair, and many need occasional maintenance afterwards. Results vary between individuals and between body areas.

Shaving is the method to use between sessions. It cuts the shaft at the surface and leaves the pigmented hair in the follicle, which is exactly what the next session needs. Waxing, plucking, threading and epilating pull that target out, and treating an empty follicle achieves nothing.

Afterwards the treated area behaves like mildly irritated skin for a short period. Heat sources, hot showers, saunas, steam rooms and vigorous exercise are usually best avoided briefly, and the area should be kept out of direct sun and protected. Follow the specific aftercare you are given, which accounts for your skin and the area treated.

Mention your medications. Some make skin more sensitive to light, some acne treatments in particular, and that changes whether a session should go ahead. This is a question the clinic should ask you, and one worth volunteering if it does not.