Urea is a naturally occurring humectant found within the skin that can be synthetically produced for use in skin care products such as lotions, creams, and anti-aging treatments.
Urea, also known as carbamide, is an organic compound produced in mammalian systems during the metabolism of proteins. The human body uses it in many processes, most notably nitrogen excretion. When your body absorbs and uses protein from the foods you eat, your liver releases urea into your bloodstream.
Urea is also a naturally occurring substance found in the surface layer of our skin, according to The Naked Chemist. It is an active part of our natural moisturizing factor (NMF), a group of hygroscopic molecules that regulate the level of moisture on our skin surface by binding water molecules in order to protect from severe drying. Urea makes up about 7% of NMF.
Healthy skin has approximately 28 micrograms of urea per square centimeter. It is known that low levels of urea leads to a decreased water-binding capacity within the skin, which in turn leads to roughness, tightness, flaking, and irritation. In fact, those that suffer from skin conditions such as psoriasis or eczema could have up to 80% less than someone with normal skin. NMF also decreases as we age.
After topical application, urea exhibits five main functions: retaining moisture, barrier maintenance, exfoliation, increasing permeability, and providing pain and itch relief.
Urea functions as a humectant type moisturizer in order to help the skin better retain moisture. A humectant is a hygroscopic substance that often has a molecular structure with several hydrophilic groups. This structure allows humectants to attract and retain the moisture in the air nearby via absorption, drawing the water vapor into or beneath the surface. This function of urea makes it a very useful ingredient for those with dehydrated skin.
The next function of urea is barrier maintenance. The skin’s natural barrier is comprised of corneocytes, ceramides, cholesterol, and free fatty acids. A strong, intact barrier is important to keep moisture in and keep things like allergens, bacteria, and irritants out. When the barrier is weakened, these intruders can pass through the top layer of skin, causing damage that ultimately leads to common skin conditions such as acne, rashes, sensitive skin, and even signs of aging. A 2012 placebo-controlled, double-blinded study published in the Journal of Investigative Dermatology found that topical applications of 20% urea improve skin barrier function and expression of antimicrobial defense in normal human skin.
Another beneficial function of urea is exfoliation. Urea exfoliates skin by dissolving the intercellular matrix of the corneocytes that make up the stratum corneum. In simple terms, exfoliation means the removal of dead skin cells. Getting rid of dead skin cells that build up on the surface of skin is crucial in order to maintain clear skin. According to Dr. Cory Torgerson, MD, PhD, FRCSC, the accumulation of extra dead cells on the skin’s surface can clog pores, eventually turning into undesirable acne or other dermal-related conditions. Furthermore, exfoliating becomes even more important as we age since the skin’s natural cycle of shedding dead cells slows down.
Urea functions as an “absorption enhancer”, which means that it improves the permeability of the stratum corneum. The enhancer effect of urea is attributed to an increase of cutaneous moisture. This function of urea can be beneficial when the goal is to help other active ingredients penetrate the skin better. However, this function of urea can be detrimental if urea is formulated with ingredients that can cause sensitization.
Finally, urea has anti-pruritic activity based on local anaesthetic effects. Thus, urea can provide local pain and itch relief when applied topically. This is especially helpful if you have a skin condition; it can break the cycle of flare-ups and uncomfortable inflammation.
The safety of urea has been assessed by the Cosmetic Ingredient Review (CIR) Expert Panel. The CIR Expert Panel evaluated the scientific data and concluded that urea was safe as used in cosmetics and personal care products. The CIR Expert Panel did note that urea can increase the percutaneous absorption of other ingredients and that this should be taken into account when conducting product safety assessments.
References: Wikipedia, “Urea”, SebaMed, “5 Ways Urea Improves Your Skin”, 2016, The Naked Chemist, “What is Urea and its Benefits in Skincare”, 2013, Wikipedia, “Humectant”, Curr Allergy Asthma Rep. 2008 Jul; 8(4): 299–305, J Invest Dermatol. 2012 Jun; 132(6): 1561–1572, Braz. arch. biol. technol. vol.50 no.6 Curitiba Nov. 2007, DermNet NZ, “Urea”, Cosmetics Info, “Urea”.