Several milk products are used in cosmetics, with the most common being goat milk, donkey milk, cow milk, horse milk, and colostrum (the nutrient-rich first milk produced after birth). These ingredients appear in soaps, creams, serums, and lotions, where they serve as moisturizers, exfoliants, and skin-repair agents. Milk’s usefulness in skincare comes down to its natural blend of proteins, fatty acids, lactic acid, and vitamins that closely complement human skin biology.
Whole Milk From Different Animals
Not all animal milks are created equal when it comes to skincare. Each species produces milk with a slightly different balance of fats, proteins, and vitamins, which is why you’ll see specific animals highlighted on product labels.
Goat milk is the most widely used whole milk in cosmetics, especially in soaps and body washes. It’s rich in fatty acids that help maintain the skin’s moisture barrier, and it naturally contains lactic acid, a gentle exfoliant that promotes cell turnover. Its slightly acidic pH sits close to human skin’s natural pH, which makes it less likely to cause irritation than harsher cleansers.
Donkey milk has a long history in skincare dating back to Cleopatra, and modern research supports some of the hype. It has a low fat content (about 1.29%, roughly 40% of cow’s milk), but a higher proportion of unsaturated fatty acids, including linoleic and linolenic acid, which are essential fats your skin can’t produce on its own. Donkey milk also contains meaningful amounts of vitamin A, which supports healthy skin cell function, and antioxidants that may slow signs of aging by reducing oxidative damage. In a clinical study of 15 healthy volunteers, a cream made with skimmed donkey milk showed satisfactory moisturizing properties and anti-aging effects compared to a placebo.
Cow milk shows up most often in processed forms like milk protein or milk powder rather than as whole milk. A soap containing 5% cow milk demonstrated good cleansing and antibacterial properties in clinical testing. Cow milk is also the primary source for many of the isolated milk proteins and lactic acid used across the cosmetics industry.
Horse (mare) milk is less common but appears in specialty European skincare lines. Formulations combining horse colostrum and horse milk have been tested for a wide range of benefits: moisturizing, smoothing, anti-irritant, oil-control, and even skin-brightening effects on healthy skin.
Colostrum: The Growth Factor Powerhouse
Colostrum is the thick, concentrated milk mammals produce in the first few days after giving birth. It’s packed with compounds that don’t appear in regular milk at anywhere near the same levels, which is why it gets its own category in cosmetics.
Bovine (cow) colostrum contains growth factors at concentrations far exceeding those in mature milk. One key example: a growth factor that stimulates cell proliferation is found at about 870 ng/mL in colostrum versus just 150 ng/mL in regular milk. Another growth factor critical for wound healing and immune cell activation is present at roughly 101 ng/mL in colostrum compared to only 4.3 ng/mL in pasteurized milk. These growth factors promote cell renewal, support wound healing, and help maintain skin structure.
Colostrum also contains immunoglobulins (immune proteins), lactoferrin (which has antibacterial and anti-inflammatory properties), and lysozyme (a natural antimicrobial). In clinical studies, a cream with 30% horse colostrum achieved complete skin regeneration in 12 patients with a type of acne. An emulsion with 20% horse colostrum reduced redness and itching in patients with moderate atopic dermatitis while softening and moisturizing the skin. For elderly volunteers, formulations containing bovine or equine colostrum improved skin elasticity, reduced sagging, and lightened age spots.
Equine colostrum has also been tested on sunburned skin, where a cream containing 20% horse colostrum and 10% horse milk provided pain relief within 24 hours and allowed a normal tan to develop without peeling.
Lactic Acid: Milk’s Star Exfoliant
Lactic acid is arguably the single most important milk-derived cosmetic ingredient, and it’s used far beyond products marketed as “milk-based.” It’s an alpha-hydroxy acid (AHA) that works by loosening the bonds between dead skin cells on the surface, allowing them to shed more easily and revealing fresher skin underneath.
What sets lactic acid apart from other AHAs like glycolic acid is its slightly larger molecular weight (90.08 versus 76.05 for glycolic acid). This means it penetrates the skin a bit more slowly, making it gentler and better tolerated by sensitive skin types. Lactic acid also has natural moisture-attracting properties, so it hydrates the skin at the same time it exfoliates. This dual action is why it’s a staple in chemical peels, serums, moisturizers, and body lotions.
While lactic acid was originally sourced from sour milk, most cosmetic-grade lactic acid today is produced through fermentation of sugars. But many brands still use whole milk or milk-derived lactic acid as a selling point for “natural” formulations.
Milk Proteins in Skincare
Milk contains two main protein families that serve different purposes in cosmetics. Casein makes up about 80% of milk’s total protein and forms a film on the skin that helps lock in moisture. Whey proteins, the remaining 20%, are rich in essential amino acids and contain bioactive compounds with antioxidant and anti-aging properties.
On ingredient labels, you’ll see these listed using standardized cosmetic names: “Milk Protein” for the whole protein, “Hydrolyzed Milk Protein” for versions broken down into smaller fragments that penetrate skin more easily, and “Colostrum” listed by that common name. Donkey milk appears simply as “Donkey Milk” on labels, following industry conventions that use the common animal name rather than a Latin species name.
Colostrum albumin, a specific protein fraction, has been combined with skin-brightening agents in formulations that showed whitening properties on skin with discoloration. Hydrolyzed milk proteins are also used in hair care products, where they temporarily bond to the hair shaft to add strength and shine.
Fermented Milk Products
Fermented milk, including yogurt and kefir-based ingredients, brings an additional benefit: probiotics and their byproducts. Fermentation changes the milk’s chemical profile, creating beneficial acids and peptides while making nutrients more bioavailable.
Fermented horse colostrum has shown promise for inflammatory skin conditions. In clinical use, it alleviated symptoms of atopic dermatitis and psoriasis while providing moisturizing and anti-inflammatory effects. Fermented colostrum also improved acne through antibacterial activity against the bacteria that colonize clogged pores.
The benefits of fermented milk aren’t limited to topical application. A study in healthy young women found that regular intake of probiotic and prebiotic fermented milk significantly increased skin hydration levels and improved skin clarity compared to a control group. The mechanism appears to involve gut health: the fermented milk reduced levels of certain compounds produced by gut bacteria (phenol and p-cresol) that are known to impair skin cell development when they accumulate in the body. This gut-skin connection adds another dimension to how milk products influence skin health.
Preservation Challenges
One reason you don’t see pure fresh milk in most commercial skincare is that milk proteins actively promote microbial growth. The same nutrients that make milk beneficial for skin also make it an ideal breeding ground for bacteria and fungi. This creates a formulation challenge that manufacturers must solve to make shelf-stable products.
Cosmetic chemists use several strategies to keep milk-based products safe. Reducing available water through ingredients like glycerol or sorbitol makes the product less hospitable to microorganisms. Adjusting pH outside the 5-to-8 range where most microbes thrive is another approach. Most commercial products also include preservative systems, often combinations of multiple preservatives that broaden antimicrobial coverage while keeping individual concentrations low. Some formulations, like the donkey milk nanoliposome cream used in clinical studies, encapsulate the milk components in tiny lipid spheres that protect them from degradation.
Fresh milk soaps sidestep this problem entirely because the soapmaking process (saponification) transforms the milk fats and raises the pH high enough to prevent microbial growth without additional preservatives.
Allergy Considerations
If you have a known dairy allergy, milk-based cosmetics deserve caution. Cow’s milk protein allergy commonly affects the skin, triggering eczema, hives, and dermatitis. While most research on milk allergy focuses on ingestion rather than topical exposure, the proteins responsible for allergic reactions (casein and whey) are the same ones used in cosmetic formulations. The skin is a recognized route for allergic sensitization, particularly when the skin barrier is already compromised by conditions like eczema. Hydrolyzed milk proteins, which are broken into smaller fragments, may pose a lower risk than whole milk proteins, but they aren’t guaranteed to be safe for allergic individuals.