Urea (overview)

Diamond of carbonic acid. White, easily water-soluble, crystalline substance which is the end product of protein metabolism in the human organism. In human urine about 30g are excreted daily.

Recipes: In recent years, urea (Urea pura) has risen to the top ten active ingredients.
Urea is also approved as a food additive (E 927b).

Keratolytic and moisturizer.

Urea is hygroscopic and forms so-called clathrates with water (inclusion compounds from which water is only released with a delay). In this property, urea is used as a moisturizer in many preparations in a 3-10% concentration. Urea shows keratolytic effects at concentrations of 20-30%. In 40% concentration urea can be used as "onycholytic".

In connection with glucocorticoids, urea has penetration-promoting effects.

From water-in-oil emulsions only a slow release of the active agent takes place. However, urea penetrates deeply into the epidermis and dermis.

From oil-in-water emulsions urea is released much faster but does not have the deep penetration effect.

Among others, desiccated skin, psoriasis vulgaris, ichthyosis, tinea unguium, s.a. tyrosine kinase inhibitors (side effects);

3-10% in emulsions, creams and ointments to hydrate the skin

15-20% in emulsions, creams and ointments for keratolysis of the skin

40% - 60% in nail softening pastes.

Standard value in serum: The standard value is between 12 and 50 mg/dl in serum or 2.5 and 8.3 mmol/l; in urine between 13 and 33 g/24h.

Skin irritations especially at higher concentrations.

Urea is unstable in solutions or water-containing formulations and gradually decomposes into its starting compounds ammonia (odour nuisance) and CO2. Cave: pH increase.

Acidic pH values, e.g. due to salicylic acid and heat, also cause increased urea decomposition (Wolff G 2014).

• Hydrophilic urea cream 5 or 10% (NRF 11.71.)
• Urea emulsion, hydrophilic 5 or 10% (NRF 11.72.)
• Urea cream hydrophilic 5 or 10% (NRF 11.71.)102
• Urea 10%/salt 3% ointment (W/O)
• Urea 10%/salt 5% ointment (W/O)
• Urea 10%/lactic acid 5% cream (NFA)
• Urea 10%/Chemicals 10% Ointment (NFA) (O/W)
• Urea paste (according to Farber)
• Urea paste 40% (NRF 11.30.)

Especially in aqueous solution or in an aqueous preparation (emulsion type: O/W) urea is unstable. It decomposes into its starting materials. Although the decomposition products are not toxic, the changed pH-value can endanger the stability of other active substances. It is recommended to add a buffer which works slightly in acid to be able to absorb the basic decomposition products. The NRF ( New Formulation Form) provides a lactate buffer for this purpose (Acidum lacticum 1% + 50% Sodium lacticum 4%).

If higher urea concentrations (e.g. 20%) are used it is recommended to use a W/O base (e.g. Eucerinum W/O base or an officinal lipophilic cream [Hydrophobic base cream DAC = NRF 11.104]).

Standard value: The standard value is between 12 and 50 mg/dl in serum or 2.5 and 8.3 mmol/l; in urine between 13 and 33 g/24h.

Pathologically increased: chronic renal insufficiency, acute renal failure, prerenal and postrenal azoteemia, marked protein intake in combination with fluid deficiency.

1. Wolf G (2009) Urea-frequently occurring active ingredient. dermatologist 60: 86-87
2. Wolf G (2013) Polypragmasia in formulations. dermatologist 64: 418-419
3. Wolf G (2013) Individual formulations with ready-to-use dermatics. Dermatologist 64: 882-883
4. Wolff G (2014) Complex interactions between active ingredient and base. Dermatologist 65: 486-487