Over-Night Biological Peel
1.7 fl. oz. for $46
Last Updated:12.16.2014
Jar Packaging:No
Tested on animals:Yes
Review Overview

Over-Night Biological Peel is supposed to be as potent as a 10% glycolic acid product, but it contains no alpha hydroxy acids, or beta hydroxy acid for that matter. Instead, this water- and silicone-based fluid contains urea, which is indeed an exfoliant, albeit a far less sexy version than AHAs or BHA because it’s derived from urine (though most cosmetic companies use a synthetic version). Urea definitely has exfoliating and water-binding properties when used on skin, and unlike AHAs and BHA, its efficacy is not pH-dependent. Much as AHAs do, it can cause a stinging sensation on application. Urea can be beneficial for those with dry skin because, although the manner in which it works isn’t fully understood, it has proven very effective at reducing moisture loss from the epidermis (Source: Dry Skin and Moisturizers Chemistry and Function, Loden & Maibach, 2000, pages 235–236). Kiehl’s ingredient list also points to HEPES as an enzyme activator. However, this ingredient (hydroxyethylpiperazine ethane sulfonic acid) functions as a buffering agent, which should help reduce any potential irritation from the urea. Although this peel is pricey and not necessarily superior to an AHA (or BHA) product, it is nevertheless a novel approach to exfoliating skin if you’re curious to try something different, or if your skin has not responded favorably to AHA products.


Stimulates skin’s biological exfoliation process-for noticeably smoother, more even and vibrant skin by morning. With first overnight application, skin texture is noticeably softer. Diminishes the visible effects of free-radical and photo-damage over time. Helps reduce the appearance of dark spots and hyperpigmentation with continued use. Performs as well as a potent 10% Glycolic Acid leave-on chemical peel-as prescribed by a dermatologist.


Water, Cyclopentasiloxane, Urea, Hydroxyethylpiperazine Ethane Sulfonic Acid, Glycerin, C12-15 Alkyl Benzoate, Propylene Glycol, Cetyl PEG/PPG-10/1 Dimethicone, Bis-PEG/PPG-14/14 Dimethicone, Triethanolamine, Phenoxyethanol, Sodium Chloride, Sodium Hyaluronate, Sodium PCA, Methylparaben, Propylparaben, Ethylparaben, Isobutylparaben, Butylparaben

Brand Overview

Kiehl's At-A-Glance

Strengths: Kiehl's staff is generous when it comes to providing samples and product information; some good cleansers; a couple worthwhile serums.

Weaknesses: Expensive for what you get; the Blue Herbal and Facial Fuel products are terrible; no products to successfully address skin discolorations; the toners are disappointing; the self-tanner should be avoided; jar packaging weakens several of the formulas.

This line has been around for quite some time, and has its origins in a family-owned pharmacy based in New York City. Perhaps its neighborly beginnings with a big-city heritage are what propelled Kiehl's to its long-standing status as a popular product line. Considering that Kiehl's doesn't advertise (at least not in the traditional sense, though their products get frequent press), their brand identity and status in the minds of consumers are impressive.

What gets lost in all the fashion magazine hype and company claims of "excellence" and "quality ingredients" is that almost all of the Kiehl's products hardly warrant excitement or even mild enthusiasm. Most of them are surprisingly ordinary, with a dusting of natural ingredients almost always at the very end of the ingredient list, well after the preservatives. That amounts to little more than a token attempt to make the products appear more natural to those who want to believe a plant or vitamin must somehow be better for the skin than something that sounds more chemical. Nevertheless, that token amount is enough to allow Kiehl's to brag about how its products nourish the skin or are more environmentally friendly, when they're not.

Aside from the allure of the natural, this line consists of totally ordinary and often completely unnatural ingredients. More disheartening for skin is that many of the ingredients are of questionable benefit for those with sensitive, oily, or blemish-prone skin. In some instances product ingredients are irritating for any skin type, while half of the sunscreen products are a serious problem for reliable sun protection. If you can't resist the allure of Kiehl's, just know that the product assembly will work best for those with dry to very dry skin and that, for the money, most of the formulas aren't knock-your-socks-off thrilling.

Note: Kiehl's is categorized as a brand that tests on animals because its products are sold in China. Although Kiehl's does not conduct animal testing for its products sold elsewhere, the Chinese government requires imported cosmetics be tested on animals, so foreign companies retailing there must comply. This requirement is why some brands state that they don’t test on animals “unless required by law.” Animal rights organizations consider cosmetic companies retailed in China to be brands that test on animals, and so does the Paula’s Choice Research Team.

For more information about Kiehl's, owned by L'Oreal, call (800) 543-4572 or visit www.kiehls.com.

About the Experts

The new Beautypedia Team proudly and unequivocally maintains the commitment to help you find the best products possible for your skin. We do this by relentlessly pursuing and relying on published scientific research so you will have unbiased information on what works and what doesn't-and the sneaky ways you could be making your skin worse, not better!

The Beautypedia Team reviews all products using the same research, criteria, and objectivity, whether the product being reviewed is from Paula's Choice or another brand.

Member Comments
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Can this product give a deep exfoliation like a AHA or BHA product? Here in Brazil there are only the Blemish age defense by Skinceuticals and the Derm AHA by La Roche Posay, both with high amounts of alcohol...

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Beautypedia Team Response

Hi there! Although this will exfoliate skin's surface and promote a noticeably smoother texture, we wouldn't categorize it as a deep peel. Such peels are best done at a dermatologist's office, not at home, as it's just too easy to overdo it and end up damaging your skin.

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