Medical Uses of Urea
Urea is primarily used as a topical keratolytic and emollient agent for treating hyperkeratotic skin conditions, and systemically for managing hyponatremia due to SIADH.
Topical Dermatological Applications
Primary Indications
Urea functions as a keratolytic agent at concentrations ≥10% and as a moisturizer at lower concentrations 1, 2. The FDA-approved indications include 1:
- Hyperkeratotic conditions: dry/rough skin, dermatitis, psoriasis, xerosis, ichthyosis, eczema
- Keratotic disorders: keratosis pilaris, keratosis palmaris, keratoderma, corns, calluses
- Nail conditions: damaged, ingrown, and devitalized nails
- Wound care: debridement and promotion of healing where necrotic tissue, infection, or eschar retards healing
Mechanism and Dosing
Urea dissolves the intracellular matrix, loosening the horny skin layer and promoting shedding of scaly skin 1. For keratolysis, concentrations of ≥10% are required, with up to 40% used for localized thick hyperkeratosis such as joints or palmoplantar keratoderma 2, 3. Application is typically twice daily, tapered as needed 1, 2.
Critical Age-Related Safety Considerations
Urea should NOT be used in the neonatal period except on very limited areas like palms and soles 2. The 2025 guidelines specify that urea ≥10% is not recommended before age 1 year, except once daily on limited areas 3. This restriction exists because:
- Epidermal barrier defects in congenital ichthyoses
- Immature stratum corneum in infants
- Higher body-surface-to-mass ratio increases systemic absorption risk
- High blood urea concentrations have been documented in collodion babies and infants with lamellar ichthyosis after topical application 2
Common Pitfalls
Avoid application on the face, flexures, and fissured areas as urea may cause irritation, itching, or burning 3. Unlike salicylic acid and lactic acid (which are strictly contraindicated under age 2), there are no reports of life-threatening toxicity from urea in children, making it relatively safer when age-appropriate precautions are followed 2.
Systemic Use for Hyponatremia
SIADH Management
Oral urea is effective for treating hyponatremia due to syndrome of inappropriate antidiuretic hormone secretion (SIADH) 4, 5. A 2024 meta-analysis demonstrated that urea significantly increases serum sodium by a mean of 9.08 mmol/L (95% CI, 7.64-10.52) 4.
Efficacy by Severity
The treatment effect varies by baseline severity 4:
- Severe hyponatremia (<120 mEq/L): increase of 18.04 mmol/L
- Moderate (120-129 mEq/L): increase of 7.86 mmol/L
- Mild (130-135 mEq/L): increase of 8.00 mmol/L
Comparative Effectiveness
Urea performs comparably to fluid restriction and vaptans, but is superior to no treatment 4. The 2014 European Clinical Practice Guidelines recommend urea for SIADH treatment 6. Urea may be particularly valuable in resource-limited settings or when other treatments are contraindicated or poorly tolerated 4.
Safety Profile
No cases of osmotic demyelination syndrome (ODS) have been reported with urea treatment 5. The most common adverse event is poor palatability/distaste, with minimal non-systemic side effects 4, 5, 7.
Additional Clinical Utility
Penetration Enhancer
Urea functions as a penetration enhancer when combined with other medications, including anti-inflammatory and anti-fungal drugs 8, 7. This property makes it valuable in combination therapies for various dermatological conditions.