Personally, I am going the conservative route and avoiding ingredients that have not been proven to be safe in pregnancy. You can decide for yourself (in conjunction with your OB or dermatologist) how conservative you want to be regarding ingredients. I'm lucky in that I can cheat and look up an ingredient's pregnancy category in a drug book (my favorite is Lexi-Comp if that makes a difference to you). Dermatologist Dr. Ellen Marmur, whose book Simple Skin Beauty I wrote about a few days ago, says "be on the safe side and ask your ob/gyn about anything that you think might be harmful." I also want to add that even if you've been reassured that something is safe, if it makes you uncomfortable, just avoid it. There are so many products on the market now, it should be easy to avoid an ingredient. It isn't worth losing sleep over!
My list of ingredients to avoid while pregnant:
• Retin A/Accutane, Retinoids, Vitamin A: Yes, the big baddies here are definitely the 2 prescription drugs listed first. Accutane is a huge issue with pregnancy as it is linked to many different birth defects. In fact, most physicians won't even prescribe it to women of child bearing age unless they are also on birth control or sign a waiver. While Retin A and over the counter retinoids are not as strongly linked to birth defects as Accutane, they are all the same class of drug and as such are on pretty much every MD's list of no-no ingredients. The retinoids are Vitamin A derivatives, and I've seen quite a few lists advising to avoid topical Vitamin A as well, so it's made my list. Yes, there is still Vitamin A in your diet and your prenatal vitamin. It should be there and can take care of your needs. But, no need to add even more in skin care.
• All Hydroxy Acids: From citric acid to salicylic acid, pretty much all of the hydroxy acids either are not safe or simply don't have enough information to say "sure, go crazy and rub this all over you." So, the official word is that all of they hydroxy acids, alpha and beta, have pregnancy categories that recommend avoidance, with 1 exception.
The exception is Lactic Acid, which your body makes on its own (I spend a lot of time in the PICU trying to prevent little bodies from making it, but that's a whole different issue). Lactic acid has been shown to be fine in pregnant animals, but we don't have evidence in humans. So, the official recommendation is to use with caution if really needed. Personally, I'm avoiding it in everyday skin care items but did let my esthetician use it in my facial a few weeks ago.
I've seen a few books that say Glycolic Acid is fine, and there are many physicians that tell this to their patients. However, its official pregnancy category is that there isn't enough info so should be avoided. The "correct" type of study to prove the safety of Glycolic Acid will simply never be done, so many physicians have looked at the current evidence and feel fine recommending it. I personally avoided it while pregnant and it's one I look for when recommending products as safe or not.
I also want to point out that Citric Acid is found usually in very small amounts at the very end of ingredient lists. It is typically there to help modulate pH in a product. You likely expose yourself to more Citric Acid in one glass of OJ than you would in a year of using such a product. I avoided it in my first 2 trimesters, but lightened up in my third trimester when I realized I was being a bit silly.
• Dihydroxyacetone: Also known as DHA, this is the active ingredient in sunless tanners. The jury is still out on whether sunless tanners are safe. I've seen sources that say yes, some that say no. I can tell you that my skin has taken on some interesting dry patches while pregnant, and it would be pretty hard to get an even sunless tan. This is a great time to embrace the pale, so I'm going with that.
• Hydroquinone: Though I found it in several drug references as safe in pregnancy, these ingredients were listed on enough lists of things to avoid due to unknown risks that I'm avoiding them.
• Kojic Acid: This ingredient is sometimes used to help lighten the skin, but it has shown up on multiple lists of items to avoid. I can't find the reason why, but I'm thinking lightening my skin shouldn't be a priority now anyways.
• Benzoyl Peroxide: Again, I can't find this in any actual drug reference books and a literature search didn't turn up anything of use, but it is listed over and over on lists of things to avoid while pregnant. Which is pretty horrible since that leaves pretty much nothing to treat blemishes during pregnancy.
• Laser Therapy: I've seen laser therapy, whether for zapping away birth marks, tattoos or hair, listed over and over on lists of things to avoid while pregnant. Even my beloved Silk'n Sens Epil lists pregnancy as a contraindication for use. I had to stop using it as soon as I found out about the pregnancy. As well, most places that offer lasers refuse to treat you if you are pregnant. Personally, I can not think of a physiologic reason why lasers would be bad during pregnancy. A laser pointed at your shin isn't going to somehow bounce the light up to your uterus, and there aren't any known systemic effects of lasers. Dr. Marmur agrees with me, in her book she says "Lasers, however, are safe during pregnancy because they don't introduce a chemical into your body."
• Salicylates: I'm adding this in as an addendum (7/6/2012) because it didn't really dawn on me to include these! I think of Salicylates as a medication to take orally (aspirin!) rather than a topical ingredient. Regardless, this should include topical willow bark and should be avoided.
• Parabens and chemical sunscreens: since that seems to be asked over and over. They are currently considered safe by pretty much everyone except the EWG, who have a big propaganda machine and I don't think they interpret most studies correctly. If you disagree with me about that so be it, I'm just stating my opinion since I've been asked over and over. Both are also considered safe for pregnancy and breast feeding. BUT... if an ingredient makes you uncomfortable you should just avoid it. There are so many products on the market these days that it is very possible to do so without any issues.
• Hyaluronic Acid use during pregnancy: Hyaluronic acid is basically the same thing as Sodium Hyaluronate. I can't figure out how this became an ingredient that is sometimes on no-no lists, because not only does your body already make a ton of it, but is a big molecule. Huge. It is so large that it just hangs out in the spot where it is made, much to large to get into cells, to pass through membranes or travel to other locations. Much is the same for any Hyaluronic Acid that you apply to the surface of the skin. Your skin has very tight membrane junctions between those cells on the surface. Hyaluronic Acid can't get through and just sits there. I'm always very suspicious when a company tells me that their HA is different and can get it. It's a big red flag. So, since it can't get in, and your body is already making it anyways, definitely feel that it is safe to keep using HA in your products. It just sits on the surface and helps hold moisture there. We need it to live up to pregnancy glow expectations!
• Sulfur: This is often found in acne treatments, and I haven't really been able to find much info about safety in pregnancy. Be aware that if you're allergic to sulfa drugs you should avoid this ingredient, but I've seen it as the active ingredient in many "pregnancy safe" acne treatments and is probably fine.
To Avoid While Breast Feeding:
A great book for looking up whether you should avoid a particular medication during pregnancy is Medications and Mother's Milk, which is updated every 2 years. This was the book we used in my residency and our lactation consultant did carry it around everywhere with her! Luckily, most medications are fine to use, and this translates over to most topical products as well. L1-L3 are considered safe, L4 and above is not safe. I also looked up each drug in the book Drugs in Pregnancy and Lactation, which is even more complete.
• Retin A/Accutane, Retinoids, Vitamin A: Used topically, Retinoids are a category L3, but orally (as with Accutane) they fall to L4. So, topical is ok, systemic is not. The second book seemed to agree with this as well, though they were more complete in listing all of the systemic (oral and IV) retinoids, things I've never heard of. Many of those were fine, surprisingly enough. I'd check with your doctor if you're on anything other than just a basic, over the counter topical retinoid, but those found in skin care products should be fine.
• Hydroquinone: While there is no data on Hydroquinone in humans, and no studies have found the levels achieved with topical use, hydroquinone is likely safe to use during nursing. Why? The ingredient is a strong base, which means the drug that actually reaches your bloodstream would be ionized and therefore unavailable to be excreted into breast milk. Which is great, because I have some Melasma to treat!
• Pretty much everything else: Safe!
If you're curious about which products are safe to use during pregnancy or breast feeding, check out my post on Skin Care Products to use during pregnancy or while nursing