Stretchmarks, and scarred skin are both representative of skin that has experienced damage in deeper layers and connective tissues. As such, they both react in a similar manner to self tanner use. You would treat them both in the same manner.
A sunless tan product is a transparent/translucent color, creating a sheer wash of color on the skin surface. It is not opaque like a thicker make-up or foundation product. Foundations, depending on thickness and opacity, can often be used to effectively hide imperfections, skin discoloration, and even fill in over large pores and dimpling of fine lines. This is due to the denser pigments used in these products and their thicker formulation that stays on the skin surface, much like a coating of paint coats a wall. Wall paint is thick, opaque, and can mask or hide the wall surface, and to and extent, fill in unevenness, and even cover some stains.
Sunless tanners are a sheer wash of color, that change the actual color of the dead skin cells on the skins surface. The tanning solution is washed away from the skin, leaving the tinted skin behind. This is a transparent coloring, that is part of the skin surface. As such, the clients skin will always show through the tanned coloration, because the skin surface is still always visible. It is not “painted-over”, but has a watercolor of sheer color tint applied.
Most scarred skin will not absorb sunless tanning solution evenly, or at all. Nor will it usually develop a brown sunless tan. Varientcy depends on scar depth, thickness, color, amount of damage, and how evenly it has healed, as well as clients skin-type and pigmentation level..
The same applies to stretch marks. After the scars or stretchmarks age and turn white or silver, they can become more absorptive toward the solution. So an older scar or stretchmarks “may” absorb some solution. Others remain eternally pale. This is 100% dependent on the client, not on the tanning product you use.
I have surgical scars that absorb no solution at all. Scars are pale white, some are also pink. Ages range from 20 plus years, to 3 years. I am a skintype 2, which normally indicates a skin type in which deep scars will stay red or pink for many years before slowly turning to white. Some have mild keloid formation (or raised areas of healing).
I also have some thinner smaller scars received in childhood, that are less visible in adulthood. They are not as visable on pale skin, unless you know where to look. They do absorb self tanner much like surrounding skin thorough a bit lighter.
Most of my stretchmarks absorb no sunless tanner, though sometime solution will pool in the deeper ones, making them look a bit darker. But they are not really tanned. Mine are over 30 plus years, and are white, and silver, but thinner and most are fairly shallow, as opposed to wide or raised or deeply sunken. I have some that are deeper, but they also do not tan.
Occasionally you will find scars that prove to be an exception, and may actually get temporarily darker from sunless tanners. They are absorbing to much solution.
Options to help scars and stretchmarks appear less prominent
If the damaged skin is in a visible area, first perform a solution spot test. This will enable you to judge how each scar is affected. (Apply some solution liberally to the area with a saturated cotton ball/pad. Let develop for 8 plus hours, and rinse. Check for color absorbancy.) Different body areas and scars or marks may not all respond in exactly the same manner. This is normal.
As long as skin and tissues are completely healed, and neither tender nor sensitive. You can spray directly over them. A scar may take as long as six months to a year for complete healing. It will often change through the years, both in texture, color, and appearance, even with no further treatment. If the area is treated with over the counter products, Laser treatments etc. the changes may occur faster or be more dramatic. Do not spray tan skin while client is ongoing laser treatments, as skin must be pale and untanned for best results.
Over the counter treatment products (acids, creams, retinoids, bleaching agents etc) will effect the skins exfoliation, coloration, and tan fade rate, increasing the tans fade off, and making it appear more uneven. You may spray the area, but advise client that the tan is less likely to appear smooth and even, nor will it fade in the same manner as untreated skin areas. Some treatments can increase skin sensitivity. Do not spray areas that become sensitive.
If the scar is fresh and still healing, avoid it while spraying. You can cover area with gauze, and “paint” solutions up to the edges of the scar, with a cotton swab.
Stretchmarks age with time, and through the years will normally become less pronounced, though most never completely fade away. For those that absorb some color from the self-tanner, they may “blend” into surrounding skin a bit. Though not completely hidden, they may appear less noticeable. But this is completely dependent on clients skin permeability, age of the stretchmarks etc.
This is not something you can predict with any confidence, until you work specifically with the client, and do some test swatches to see how their individual skin reacts. Please never tell a client that spray tanning will hide their stretchmarks, scars etc. This is a guarantee you really can never make, and at some point a client will feel you have intentionally deceived them, even though your intentions may have been completely well-meaning.
For many clients, this can be an area of discomfort, and embarrassment (though it never should be) and a number of clients are very distressed over the appearance of scars or stretch-marked skin. It can be a very emotional issue, and can be very upsetting when a client feels they have been extended false hopes.
Stretchmarks are 100% normal, and very common in all ages, fitness levels, and both Men and Women experience them. They are NOT something one should ever be ashamed of, they are natural and a part of life. Believe it or not, many super thin and super fit Models and athletes wear some of their own. The always beautiful Chrissy Teigen embraces hers HERE.
They occur from normal growth, puberty, weight changes, and are common in pregnancy. But even if one has never experienced pregnancy, they may have stretch marks.
Using a darker sunless tanner will not normally make them “more hidden” and in some cases could make them temporarily more visible, if they stay white/silver, and surrounding skin becomes very dark. If scars or stretchmarks are red or pink, they will blend in more with surrounding “tanned” skin as the pale skin will be darkened closer to the color depth of the pink or red damaged skin. They will still appear pink or red, but the contrast may be less distinct.
For photo shoots, celebrity’s and models would normally use a self tanner, and then apply a Body make-up product to all visible skin to further hide and blend scars, stretchmarks, tattoos etc.
Additional photo editing is then done with computer generated software programs on the final photos.
Sally Hansen Airbrush Legs is an example of a Body Makeup that can be used in theis manner. This comes in sprays or lotions, though many other similar products are also avaiable. Even a thicker facial foundation can be used in this manner, set finish with a translucent powder to limit transfer.
https://www.sallyhansen.com/us/airbrush