Misleading Beauty Advice

I am bidding on some vintage beauty books and magazines (my obsession) on Ebay, and it made me think of all the ridiculous beauty advice that's been given over the years. There's even a book about the subject, called Peculiar Beauty, that I highly recommend. It's a compilation of the silliest, zaniest bits of advice from old beauty books (some as recent as the 80s, and some going way way back). While no one has given me any truly humorous advice, I've definitely been the recipient of some misinformation. Usually, I know enough to separate fact from fiction, but even a former beauty editor can be misled by someone who seems knowledgeable.
Fortunately, I knew better than to believe some of the "advice" given to me by my former aesthetician. Now, let me start by saying she was amazing. She was Eastern European, as all the best ones seem to be, and she gave me the most thorough facials. But that doesn't mean she was infallible. Once, while she was raving about a tinted moisturizer from Aveda, I commented on the low SPF, and she said it was okay, because since the tinted moisturizer had an SPF of 8, and her regular every day skin cream had an SPF of 10, it was like she was wearing an SPF of 18, because it was cumulative. This is NOT true. Basically, all this gets you is the higher SPF, in this case, a 10. She also told me about a product that contained a retinol, and said it's the same thing as Retin-A. This is impossible, of course, since Retin-A is a retinoid and available only by prescription, whereas retinol, also a vitamin A derivative, is a much less potent ingredient and available over the counter.
The moral of this story: Don't believe everything you hear. Check with someone you respect, like your dermatologist.