Urea
Keratolytic and moisture-binding active ingredient in dermatology
Urea (Latin: urea) is an organic compound that naturally occurs in the human body as an end product of protein metabolism and is excreted by the kidneys. In dermatology and pharmacy, urea is used as a topical active ingredient combining two key properties: a keratolytic effect (dissolution of excess keratin in the stratum corneum) and a pronounced moisture-binding capacity (humectancy). This combination makes it one of the most frequently used ingredients in creams, lotions, and ointments for dry, scaly, or thickened skin.
Urea is available in different concentrations, with the concentration determining the therapeutic focus: low concentrations of 2 to 10 percent act primarily as moisturisers, medium concentrations of 10 to 20 percent additionally as keratolytics, and high concentrations from 20 to 40 percent are used specifically for the treatment of heavily keratinised skin or certain nail conditions. The active ingredient is found in numerous finished preparations such as Eucerin, Laceran, or Elacutan, as well as in individual formulations.
Mechanism of Action
The effect of urea on the skin is based on several biochemical and physical mechanisms. As a small, hydrophilic molecule, urea penetrates the epidermis and binds water molecules in the stratum corneum. This effect significantly increases the water content of the horny layer, resulting in softer, more supple skin. Urea thus belongs to the natural moisturising factors (NMF), which are also physiologically present in healthy skin.
The keratolytic effect arises through the denaturation and dissolution of hydrogen bonds in the keratin matrix. Urea weakens the intermolecular bonds between keratin filaments, thereby facilitating the detachment of excess horny layers. At higher concentrations of approximately 20 percent or more, the natural desquamation process is also accelerated, enabling the treatment of hyperkeratotic skin changes.
A further aspect is urea's ability to increase the permeability of the stratum corneum barrier. This is therapeutically relevant because it acts as a so-called penetration enhancer, transporting other active substances (e.g. corticosteroids or antifungals) deeper into the skin. In combination preparations, this effect is deliberately utilised.
Indications
- Dry and scaly skin (xerosis cutis): Most common indication, particularly in patients with diabetes mellitus or chronic renal insufficiency
- Ichthyoses: Genetically determined keratinisation disorders with pronounced scaling; urea is considered a standard therapeutic agent
- Psoriasis: Supplementary basic therapy for softening and removing scales
- Atopic dermatitis (eczema): Moisturising care as an important pillar of basic therapy
- Nail mycoses and onychogryposis: Highly concentrated urea preparations (40%) for softening and atraumatic removal of diseased nail portions
- Hyperkeratoses: Calluses, hardened skin on heels and soles (keratosis palmoplantaris)
- Lichen pilaris (keratosis follicularis): Pronounced follicular keratinisation disorders
- Pruritus (itching): In dry skin; urea can relieve itching through rehydration of the stratum corneum
Dosage and Application
2 to 5 percent urea: For daily basic care of mildly to moderately dry skin; suitable for large-area application, also on the face (if specially formulated). 10 percent: Standard concentration for body lotions and creams in significant skin dryness and early hyperkeratosis; apply once to twice daily. 20 to 30 percent: Ointments or creams for pronounced hyperkeratoses, ichthyoses, and psoriasis plaques; apply to moist skin after washing. 40 percent: Nail treatment; usually applied in the form of nail plasters or occlusive dressings over several days to soften diseased nail portions.
As a general rule: apply the preparation evenly to the affected skin areas and massage in gently. Urea is not suitable for open wounds, severely inflamed, or weeping skin lesions, as burning and irritation may occur. In the face and on mucous membranes, only specially formulated products with low concentrations should be used.
Side Effects
Locally common: Burning, stinging, or tingling immediately after application, particularly with higher concentrations or on irritated skin. These reactions are usually transient and subside after a few minutes.
Occasional: Local redness (erythema), itching, dry feeling after absorption. In sensitive skin or application to inflamed skin, irritation may be more intense.
Rare: Contact allergies to urea itself are very rare; patients more frequently react to excipients such as fragrances or preservatives in the formulation. With large-area application under occlusion and high concentration, a small amount of systemic absorption is possible, which is, however, usually clinically insignificant.
Interactions
Urea itself shows virtually no systemic interactions, as it is applied topically and only minimally absorbed. However, its property as a penetration enhancer is relevant: the simultaneous application of urea with other topical active substances can significantly increase their absorption. With highly potent corticosteroids, this can lead to enhanced systemic effects, which should be considered in therapy.
In combination preparations with corticosteroids, antifungals, or keratolytics such as salicylic acid, this enhancement of active substance penetration is often therapeutically desired and deliberately utilised.
Special Notes
Pregnancy and breastfeeding: Urea is considered safe for topical use. Due to its natural occurrence in the body and the low systemic absorption with intended use, no risks for mother or child are known. Nevertheless, large-area application of highly concentrated products during pregnancy should be coordinated with the treating physician.
Children: Urea can also be used in children; however, products with high concentrations should only be used in children from a certain age (usually from 3 months). In infants and toddlers, concentrations of 5 percent and below are preferred.
Diabetes mellitus: Patients with diabetes are particularly frequently affected by skin dryness and foot calluses. Regular urea care of the feet (10 to 20%) is considered an important component of diabetic foot prophylaxis.
Storage: Urea preparations should be stored cool and dry, as urea hydrolyses to ammonia and carbon dioxide at higher temperatures (decomposition). The expiry date must be observed.
Frequently Asked Questions
Can urea be used daily on the skin?
Yes, urea products in low and medium concentrations (up to 20%) are suitable for daily use and are even recommended for chronically dry skin. They replace natural moisture-binding substances that are reduced in dry or diseased skin.
Why does urea burn on the skin?
Burning occurs when urea comes into contact with cracked, inflamed, or very dehydrated skin. As the skin regenerates, this sensation usually diminishes. With very severe burning, a switch to a lower concentration is recommended.
Difference between urea and salicylic acid?
Both substances act as keratolytics. Urea is additionally a humectant and binds water; salicylic acid has a stronger anti-inflammatory and antimicrobial effect. Both can be combined, which enhances the keratolytic effect.
Is urea available without a prescription?
Yes, many urea products up to 20 percent are available without prescription at pharmacies. Highly concentrated preparations from 40 percent for nail treatment are generally dispensed on prescription or on medical recommendation.
References
- Product information for urea preparations (Eucerin, Laceran, Elacutan), as of 2024
- Guideline for the treatment of ichthyoses by the German Dermatological Society (DDG)
- European Medicines Agency (EMA): Information on topical keratolytics
- Mast A et al.: Urea in Dermatology. Journal of the European Academy of Dermatology, 2023
- Federal Institute for Drugs and Medical Devices (BfArM): Monograph Urea