There is a lot of controversy around tanning, its benefits and downfalls and if there are any worth wile positive sides to it.
One thing is for certain though, when you tan, your skin color darkens a certain amount (more if you have fair colored skin) on its first layer.
When this happens, your skin becomes darker than your original color, but not your stretch marks, since the stretches are not in full working condition. So in most cases, when too much tanning is done, the scars actually stand out more due to them being the same color as before and not changing much with the skin.
So you end up looking like a brownish tiger with red or white stripes.
2 Factors That Decide If It Helps Or Not
What makes the biggest difference whether it will look better or worse, is your striae age and your skin color.
If your stretch marks are young, they will be closer to the color red, which stands out a lot and when you add the tan, it will stand out even more. In the other case, where you have had your scars for some time now, they have turned to a color closer to white they will also normally stand out even more, as they will always be white.
And while they will stay white, your skin will darken, resulting in a dark skin with white stretch marks. Not a good thing if you want to hide your scars. But know that all of this has no effect at all if your skin color is of a darker tint as some skin colors in the middle can successfully hide any skin impurities just by their color.
For example, if you have darker stretch marks, and your skin color is very pale, tanning will darken your skin enough so that it will actually improve how you look. In the long run, tanning is not recommended if you have striae as most people (in other words, more than 90%) report bad results and only rarely does someone with a darker skin tone report an improvement.
You could however, use some sort of concealer for your stretch mark to make it closer to your tanned color.
What is recommended, not only for scars, but medically speaking as well, is to tan in moderation.
When doing so, always remember to use sunscreen with a enough of SPF as the sun can, if exposed to it too much, destroy the collagen that your skin has been working hard to produce, actually hindering your progress. This is why it is important to never tan if you are using a stretch mark cream of any kind.
If not careful, the tanning can negate much of the progress that your skin was making. Just to warn you, if you have any other skin condition (acne, rashes, etc.) other than scars, see a doctor and get the OK from him, so you can tan without worry of making things worse.
Just a side note..
Also, you might have heard tanning salons mentioned somewhere.
Numerous studies such as this one all suggest that tanning can be very damaging to your health.
Instead, when the season comes, expose yourself to the sun in smaller amounts (when it is not at its strongest) and you will get a nice tint to your body without any excessive damage. This makes it a win win for everyone, you get your nice looking tan and possible stretch mark fading, plus your body doesn’t get damaged in the process. Everyone wins.