Keratolytics and Their Properties

Keratolytics and Their Properties

The term “keratolytic” comes from the Greek language and means breaking down the corneal substance. These are drugs that soften, dissolve, and help shed the thickened layer of keratin in the upper layer of the skin.

Keratolytics are divided into three groups:

  1. Alkaline (Alkalis)
  2. Acidic
  3. Urea (or Carbamide)-based


These are the most common drugs that work quickly. The effective pH range in these products is 10.5 – 12. The higher the pH values, the more effective the alkaline keratolytics are in breaking down keratin. Alcohol, glycerin, propylene glycol, polyethylene glycol, and others enhance the keratolytic activity of alkalis.

Recently, alkalis have also been combined with various surface-active agents such as laureth sulfates. These substances help moisturize and disperse the corneal layer in the initial stage of drug action, opening the door for the alkalis to work. This approach allows achieving clear results at lower concentrations and pH values.

But there’s another side to the story. Alkalis are highly potent softeners and require precise washing or neutralization using special means. When they reach intact skin, they continue to have their harmful effect. As a result, we see “glass heel,” peeling skin prone to damage, and damaged nails. For specialists, alkali-based drugs also affect poorly: they spoil the skin of the hands, and when they enter the respiratory system, they lead to internal health disorders.

For those experiencing issues (sensitive and delicate skin, damage to skin layers, diabetes, etc.), the use of alkaline softeners is prohibited.


Alpha and beta hydroxy acids have been used in cosmetics due to their excellent keratolytic effectiveness in foot care. If the effectiveness of alkalis as keratolytics depends on the formation of alkaline albuminates (a type of alkaline protein reaction products), acids as keratolytics work by another mechanism.

Changing the protein structure and breaking it down after exposure to acids makes it unable to return to its initial modification. We can observe this phenomenon as “frosting” – the formation of whitish oval spots on the skin surface during acid peeling.

The practical range of acids is pH 2-4, where pH 4 is considered a very mild acidic keratolytic.

So, what is the mechanism of acids’ effect on the skin? When acids affect the skin, depending on the concentration and exposure, they dissolve the cornified cells in the upper layers of the skin, and sometimes even the entire skin, down to the basement membrane. In other words, when applying an acidic mixture, we obtain a controlled chemical burn of the skin.

Fruit acids and some other acids have exfoliating properties. In response to intensive exfoliation, there begins active division of basal layer cells, leading to skin thickening.

The theory of pressure explains also the intensified stimulation of substance synthesis between cells in the skin. In response to pressure, the skin moves, and the repair activity of skin cells increases, accelerating the synthesis of essential vital molecules. The result will be skin thinning and an increase in skin layer thickness.

Like alkaline keratolytics, acidic keratolytics carry many warnings and require the use of standards to restore skin pH balance.


Urea, also known as carbamide, is perhaps one of the most common ingredients in foot care products, and it’s not without reason. It’s hard to find another ingredient that carries such diverse properties to the same extent.

Naturally present in the stratum corneum, urea acts as a natural moisturizing factor. Healthy skin contains 8 micrograms/cm² of urea. In dry skin, urea content decreases to 3 micrograms/cm², while in damaged skin, it drops to only 1.5 micrograms/cm². Advanced age, eczema, psoriasis, and atopic dermatitis are associated with low urea concentrations.

Urea plays a crucial role in retaining moisture in the skin due to its excellent humectant properties. Urea molecules are small and can easily penetrate the upper layer of the skin, binding water and thus moisturizing the skin and alleviating symptoms of “dry” skin.

Urea is interesting because it alters physiological properties depending on the concentration. In concentrations ranging from 3 to 10%, urea acts as an excellent natural moisturizer. Starting from a concentration of 10%, a mild keratolytic effect can be observed, which increases with increasing concentration.

Products with urea concentrations of 10% to 20% are excellent solutions both in salon procedures and in supportive home care. High concentrations (15-20%) are suitable for correcting serious skin lesions on the feet.

In accumulating the keratolytic effect of urea, it needs “helpers,” carriers that help it overcome the skin barrier. Alcohol and active emollients in lubricants and active emulsifiers act as helpers in keratolytic preparations, enhancing each other’s effects.

Urea opens the upper corneal layer, accelerates the shedding of dead cells from the surface, soothes the skin, reduces itching, exhibits a localized anesthetic effect, and reduces irritation. Since urea does not affect the skin’s pH balance, it does not need to be neutralized. It works safely and gently.

Urea keratolytics are mainly used in foot care offices, where individuals require cautious treatment and have warnings against using acid or alkaline keratolytics. In these cases, there are usually accompanying conditions such as diabetes, venous inflammation, cardiovascular disorders, and individuals who have undergone chemotherapy.

To make the right choice for any keratolytic, balance the “positives” and “negatives” and analyze before use. Are they all in good health and have no contraindications for using acid or alkaline keratolytics?