Sunscreen is supposed to block the harmful UV rays (the ones that burn you), whist permitting some of the less-harmful ones to get through and cause tanning (and possibly synthesis of vitamin B in your skin too). So you get to stay out in the sun longer and get more tan; some of this extra time is mitigated by the aforementioned screening, but not all.
Well, they are slightly different in the way they penetrate the skin and the kinds of things they affect when they do, but actually, on researching this a bit more; sunscreen appears to be trying to simply limit the dosage of UV; this might still result in an overall quicker tan, because it could mean that you stay out in the sun tanning slowly, rather than turn lobster-red and spend the rest of your holiday whimpering in the shade.
I could be wrong, but I think what the OP is asking is, if one wants a deep tan (and skin like leather or skin cancer many years later!) do those “deep tanning” lotions and oils do the job any faster than using nothing?
My guess is not. All they do is moisturize the skin or give you that attractive-to-some oily, glistening look.
I grew up in the era of baby oil and iodine as a “quick tanning” potion. Yikes!
Yes, this was my main inquiry. Unless the lotions or oils somehow magnify the UV rays, there’s only so much energy coming out of the sun. Most “deep” or “dark” tanning oils claim to expedite the process or allow for a darker tan than you can achieve au natural. Knowing what I know about physics and biology, I can’t see oil having a great effect*. Are millions of George Hamilton wannabees being suckered?
*I understand that there are moisturizers and vitamins in most of these formulas as well, but these are usually understood as secondary to the real intent of the product (i.e. tan accelerant).
I’ll even concede that most of your more “respectable” brands like Coppertone, seem to avoid this terminology. But I think there might be a general myth washing over the more gullible that these oils somehow magically give you a darker tan faster, while protecting your body from UV. When in actuality, it appears that unless it has an SPF factor, it’ll do nothing more than moisturize your skin and make it smell like [insert tropical fruit smell here].