Fruit acids

Collective term for a group of (organic) hydroxycarboxylic and dicarboxylic acids that occur in fruit. These substances do not have to be labelled as additives when used in food. Many fruit acids are alpha-hydroxycarboxylic acids (AHA) and some dicarboxylic acids.

Fruit acids include:

• malic acid
• Citric acid
• Fumaric acid
• Gluconic acid
• Glycolic acid
• Mandelic acid
• Lactic acid
• Oxalic acid
• Salicylic acid
• alpha-hydroxycaprylic acid
• Tartaric acid.

The term "fruit acids" originally referred only to alpha-hydroxycarboxylic acids occurring in fruits and plants such as malic acid, citric acid, glycolic acid, lactic acid and tartaric acid. Later, the term "fruit acid" was extended to include the dicarboxylic acids oxalic acid and fumaric acid, as these were also found in fruits.

A special case is the aromatic salicylic acid which belongs to the phenolic acids. It occurs in many plants but despite similar applications it also shows major differences in its effects e.g. on the human skin.

Fruit acids occur naturally in many plants, mainly in their fruits. Together with the sugars, they have a decisive influence on the special taste of the respective fruit. The total content of organic acids in fruit is about 1-3%.

Food: Fruit acids and their salts serve as acidifiers of food. Citric acid is used for preservation purposes.

Cosmetics: Fruit acids are used in cosmetics as skin peeling agents (fruit acid peeling). Besides the single acids, so-called fruit complexes are also used in cosmetics where several fruit acids are combined. The fruit acid concentration in home products is between 1 and 10% and may not exceed 10%. In cosmetic institutes concentrates of up to 40% may be used. All concentrations above this (up to 70%) require strict medical control.

During the fruit acid peeling of the skin, a superficial keratin ablation is induced by a controlled use of alpha-hydroxy acids, such as glycolic acid (20-70%), lactic acid, malic acid, citric acid, tretinoin (mostly used as an additive), salicylic acid (up to 50% in case of extrafacial application) (see below chemical peeling).

Fruit acid peelings are suitable to improve the skin texture. Treatment is carried out in several sessions, each at intervals of five to 14 days. In medical practices e.g. glycolic acid peels are started with lower concentrations of 20% to 30% and then, depending on tolerance and effect, are increased to concentrations of up to 70%. A fruit acid peeling can be combined with other procedures (e.g. microdermabrasion) under medical supervision.

Medicine: Various fruit acids are medically used in the therapy of acne vulgaris.