How Effective is Urea?
Word on the street is that the ‘hot new thing’ is rubbing piss on your face.
Piss? Surely not, that’s mental.
Yeah, I heard some kid outside of Sephora saying they can’t wait to try this new ‘Exfoliating Urine Cream’.
Urine? Do you mean urea?
Yes, I think I meant that. How embarrassing.
Today I am talking briefly about urea. Not urine. If Golden Showers are your thing, you’re in the wrong place. For now, anyway.
What is Urea?
To be fair to that person that embarrassed themselves horribly above, urea is certainly found in urine as a breakdown product of various proteins. Urea plays an important role in the cellular metabolism of nitrogen-containing compounds by most animals. It is often called ‘carbamide’ in the literature probably to get away from the pissy connotations.
Side note: I have seen numerous brands try and admonish urea as a dangerous cosmetic ingredient over the years. These brands all make the same, frankly silly mistake, of confusing urea with urea-containing preservatives which I talk about here. Unless a brand has a scientist or other technical person on board that writes or at least oversees their writing output then I would recommend taking their words with a large pinch of salt.
It presents as a colourless, odourless (thank god) solid which is highly soluble in water and virtually non-toxic based on an LD50 of 15g/KG (in rats).
For formulators, urea usually appears as small, white/transparent pearls. Urea is only very slightly basic when dissolved in water so for all intents and purposes is considered a pH neutral substance. This makes the INCI listing function of ‘pH Regulator’ a tad confusing but this refers to its stabilising action on other basic or acidic ingredients rather than a direct action on pH itself
While urea is found in your dirty excretions, it is also naturally occurs in the skin where it is considered part of the Natural Moisturising Factor (NMF) along with other humectants like hyaluronic acid, various amino acids, ceramides and other fatty acids. NMF makes up around 20-30% of the dry weight of skin cells and urea makes up around 7-10% of that, so across your whole body, there is a substantial amount of urea.
While urea is naturally ubiquitous in animals, commercial urea is entirely synthetic and was first produced from inorganic materials in 1828. As such, although urea is an organically occurring compound it cannot be used in formulas which are aiming for 100% organic certification as cosmetic urea is synthetically manufactured.
Benefits & Function
The official INCI functions of Urea are:
Skin conditioning : Maintains skin in good condition.
Antistatic: Reduces static electricity by neutralising charge on a surface.
Humectant: Maintains water content of a cosmetic both in its packaging and on skin.
pH Regulator: Stabilises the pH of cosmetics.
Urea is also a keratolytic which isn’t listed as an official INCI function. This means urea can break down the outer layers of the skin in much the same was as ingredients like Salicylic Acid although it is much less potent at comparable concentrations. It is thought that urea is able to increase the expression of key structural proteins including filaggrin and loricrin which are themselves important in keratinocyte differentiation and thus skin barrier function. Filaggrin sees the most expression immediately after urea treatment and deletions of the filaggrin gene result in conditions such as ichthyosis vulgaris, characterised by dry skin and flaking. In this way, higher concentrations of urea help to slough away dead or damaged out skin while supported healthy barrier function of new skin.
Is Urea Safe for the skin?
The concentration of urea in topical products vary dramatically depending on intended use. For moisturising action concentrations are typically in the 2-10% range, keratolytic action is observed in the 10-30% range and true therapeutic grade debriding formulas will often have 30%+. These are often used to treat severe cases of eczema, keratosis and to remove calluses. These incredibly high concentrations support repeated observations that urea is overall, very well tolerated. As expected, higher concentrations of urea lead to the greatest side effects which include irritation and redness. Due to the keratolytic action of urea, formulas containing higher concentrations are not typically suitable for sensitive skin (unless under clinical guidance), areas of broken skin or for application near delicate tissues such as the eyes. While not as innocuous as an ingredient like glycerine, urea has a very solid safety profile, especially when used at the lower and more common concentrations typically seen in the industry
How effective is Urea?
Various studies have demonstrated the therapeutic value of topical urea and high strength urea topicals are already frontline treatments for a variety of dermatological disorders:
Keratolytic: Many studies have shown that urea is keratolytic with this action mainly emerging when urea is used in concentrations of 10%+. An interesting study used ultrasound to address epidermal structural changes after an anhydrous paste application of 50% urea to patients with hyperkeratotic psoriatic plaques: essentially thickened and stubborn scaly patches of skin usually on the palms, heels and soles. 92% of the treated cohort showed clinical clearance of the plaques at treatment day 21 (out of 25). No side effects were reported at all in this study and all the patients rated the urea paste as excellent in terms of cosmetic acceptability.
Anti-Bacterial: As study from 2012 proposed that urea is not just a passive metabolite but a critical small molecule regulator of epidermal structure and function (more recent studies seem to confirm this theory). Topical application of urea increases the expression of numerous genes that code for various molecular transporters important in keratinocyte function. Interestingly, topical application also enhanced expression of various antimicrobial peptides including AMP; LL-37 and B-Defensin-2 suggesting urea may help skin set itself to ‘defence mode’ to increase clearance of harmful microorganisms. Overall the authors suggest topical urea could be a therapeutically valuable treatment option for diseased skin.
Wound Healing: Urea has been a known wound healing accelerant for decades with a paper from 1938 summarising how urea likely achieves accelerated wound healing:
a) Urea is a known keratolytic and by removing dead or dying tissue, urea removes one of the chief deterrents to healing in many types of infection.
b) It is practically non-toxic and has a very low irritant profile on living tissue
c) It is mildly bactericidal
Ultimately, urea helps create an ideal environment in which healing can take place. This is actually quite similar to how allantoin achieves its reparative action; by setting up an ideal environment for endogenous repair.
Moisturising: Various studies have shown that urea has wide reaching benefits that ultimately express as greater moisture content in the skin, largely by maintaining healthy skin barrier function. In doing so, topical urea application improves the ability of the stratum corneum to resist osmotic stress. Furthermore urea acts as an endogenous humectant, replacing water in low humidity conditions and also reducing the rate at which water is naturally lost from the skin (Interesting studies and reviews here, here and here)
What does Urea pair well with?
Urea is an interesting ingredient with different actions depending on concentration. It is an effective skin moisturiser and at higher concentrations is an effective chemical exfoliating agent. It can be combined with all manner of other ingredients as it isn’t particularly reactive.
It combines particularly well with:
Panthenol – soothing, humectant
Glycerine – humectant, moisturising
AHAs/BHAs – improved exfoliating effect, caution at higher concentrations
Summary
Urea is a cheap and readily available synthetic ingredient with a range of uses as a moisturiser, chemical exfoliator and humectant. It is well tolerated and incorporates well into many different product types.
Key Benefits:
· A gentler alternative to other chemical exfoliators
· Inexpensive as an active ingredient
· Well tolerated
· Effective moisturiser
This post was written by our Chief Scientist, Dr. Edward Jones
