Vitamins can be derived from plant or animal products or produced synthetically in a laboratory. Vitamin A, for example, can be derived from fish liver oil, and vitamin C from citrus fruits or rose hips. Unlike dietary minerals, which are elements on the periodic table, vitamins are molecules made from the elements. Vitamin C (ascorbic acid), for example, is made of carbon, oxygen and hydrogen and is found naturally in nature and can be produced by many animals – but not humans, fruit bats or guinea pigs.

The natural vitamin can be made from a component directly from the earth or it can be 'naturally made' in your body through digestion. Or, it can be a product, like a vitamin B, that begins with natural fermentation but is additionally processed. Vitamins are classified as either water-soluble or fat-soluble. In humans, there are 13 vitamins: 4 fat-soluble (A, D, E, and K) and 9 water-soluble (8 B vitamins and vitamin C).  Water-soluble vitamins dissolve easily in water and, in general, are readily excreted from the body to the degree that urinary output is a strong predictor of vitamin consumption. Because they are not as readily stored, more consistent intake is important. 

Fat-soluble vitamins are absorbed through the intestinal tract with the help of lipids (fats). Vitamins A and D can accumulate in the body, which can result in dangerous hypervitaminosis. Fat-soluble vitamin deficiency due to malabsorption is of particular significance in cystic fibrosis.

Vitamin A - Vitamin A (retinol) is diterpene alcohol that abundantly occurs in fish liver and egg yolk. There is a whole series of derivatives and provitamins:

Retinyl Acetate, Retinyl Palmitate and Retinyl Propionate are esters of vitamin A. They are enzymatically hydrolyzed in the skin. Retinal is vitamin A oxidized into an aldehyde. It occurs in the eyes and is significant for vision. Like Retinol, Retinal is oxidized in the skin into vitamin A acid.

hyperkeratoses and scars

compromised skin and acne caused by cornification disorders on the exits of the sebaceous glands

stimulation of cell growth and collagen synthesis in the epithelial tissue

ageing skin: frequently in combination with the antioxidative 

Vitamins E and C - Retinoids can cause irritations, which means that topical vitamin A acid effects such as erythema can be observed with higher concentrations and penetration supporting nanodispersions. The number of vitamin A receptors however increases with the duration of the treatment. Hence it is recommended to start the treatment with low doses and then slowly increase the concentrations.

B vitamins - Vitamin B1 (thiamin) is water-soluble and a natural ingredient of cereal and yeast extracts. In aqueous solutions, it is deactivated by heat. The decomposition products partly generate the meaty flavour which is characteristic of cooked food. As a coenzyme component, the vitamin plays an important part in carbohydrate metabolism. In cosmetic applications, it is used as a salt (hydrochloride) and frequently combined with other B-vitamins (vitamin B complex) for the treatment of compromised skin.

Vitamin B2 (riboflavin): Sources of riboflavin are yeast, milk, liver and other innards. The vitamin is involved in the formation of numerous oxidoreductases. It is used as a yellow colouring agent in food and cosmetic products.

Vitamin B3 (niacin) occurs either as nicotinic acid or nicotinamide (INCI: Niacinamide). As a component of the coenzymes NAD and NADP, hence dehydrogenases, it is found in non-processed food (meats, cereals) and involved in the biochemical redox reactions. The vitamin is reabsorbed as nicotinic acid in the intestinal tract. In cosmetic products, the amide is used for skin recovering purposes due to its better water-solubility.

Vitamin B5 (pantothenic acid): As a component of coenzyme A it is contained in milk, liver and vegetables. In the cosmetic field sometimes the calcium salt (Calcium Pantothenate) is used, however frequently the easily penetrating provitamin (D-Panthenol) is preferred which is oxidized in the skin into pantothenic acid. Fields of application are:

enhanced skin hydration

treatment of inflammatory processes

cell formation and epithelisation after skin lesions

suppression of itching

hair cures

Vitamin B6 (pyridoxine) in its original form is an alcoholic compound. Also, pyridoxal with its aldehyde function and pyridoxamine with an aminomethyl group belong to the vitamin B6. The three compounds show the same vitamin activity as they can be transformed into each other. Yeast extract, milk, seeds and nuts are typical sources of this vitamin. Pyridoxal phosphate is a coenzyme of numerous enzymes of the amino acid metabolism. Vitamin B6 deficiencies lead to various forms of dermatitis. Predominantly the hydrochloride of pyridoxine is used in skincare products.

Vitamin B7 (biotin) has an interesting double ring structure that contains a urea group, among others. The former term "vitamin H" indicates its significance for the skin. In low concentrations, it is ubiquitous in food. The highest concentration occurs in yeast. The vitamin is a key component in the enzymes of the amino acid and fatty acid metabolism. Deficiencies lead to growth disturbances of the hair, nails and skin. Consequences are loss of hair and dermatitis.

Vitamin B9 (folic acid): The yellow compound is rich in nitrogen and occurs in vegetables, liver and cereals. It plays a significant role in the C1 metabolism, i.e. in the transfer of methyl-, methylene or formyl groups, where it is effective in the form of tetrahydrofolic acid. Folic acid participates in DNA synthesis.

Vitamin B12 (cobalamin) is a macromolecule that contains cobalt and can only be synthesized by micro-organisms living in the intestinal tract of animals or on the surface of soiled food. Hence, it can only be assimilated with animal food where it occurs in concentrated form in the liver and kidneys; an exception though is the algae spirulina maxima. Deficiencies can occur in vegetarians or vegans however also pathological conditions of the intestinal microflora inhibit the resorption of the vitamin. Its use in skincare products is controversially discussed as it is assumed that the molecule is able to bind nitrogen oxide. 

Vitamin C - The water-soluble vitamin C (ascorbic acid) is sufficiently supplied with fruit and vegetables. It participates in the biosynthesis and the cross-linking of collagen but also is involved in many other metabolic activities in the field of steroids, amino acids and catecholamines. 

The main functions in cosmetics are:

Product protection (antioxidant)

deactivation of free radicals

keratolytic effects of free concentrated ascorbic acid at a low pH level analogous to the AHA acids.

prevention of hyperpigmentation

stimulation of the collagen formation

While the first three features are reliably accomplished by free ascorbic acid, the remaining two functions can only be successfully achieved by its derivatives due to the fact that free ascorbic acid tends to be unstable on the one hand and on the other hand, will practically not penetrate into the skin in the form of a polar molecule. Hence it is essential to use derivatives and carrier substances:

Ascorbyl Phosphate is applied in the form of sodium or magnesium salts. It is the water-soluble ester of vitamin C with phosphoric acid and enzymatically hydrolyzed after having passed the skin barrier. The carrier substance is phosphatidylcholine in the form of liposomes.

Vitamin D - The most significant sources of vitamin D (calcitriol) are the provitamin D2 (ergosterol) that occurs in mushrooms and wheat germ oil among others, and provitamin D3 (7-dehydrocholesterol) that is found in egg yolk, liver and fish oils. Vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol) are formed from provitamin D2 resp. provitamin D3 under the influence of sunlight. They are transported into the liver and there transformed into 25-hydroxycholecalciferol.

Vitamin E - Vitamin E is equipped with a terpene side chain that is bound to a chromane ring and belongs to the group of fat-soluble vitamins just as the vitamins A, D and K. As a natural antioxidant, vitamin E occurs in all unsaturated vegetable oils. Wheat germ oil is in top position in this regard. The outstanding physiological function of this vitamin is the protection of oxygen-sensitive cellular components such as omega-3 and omega-6 fatty acids. In the cosmetic field, the free vitamin and its derivatives are used. The derivatives are the esters of organic acids. 

Vitamin K - Vitamin K belongs to the fat-soluble vitamins and occurs in two natural forms, vitamin K1  and vitamin K2. The phytyl side chain of vitamin K1 is equivalent to a monoterpene with 20 C-atoms. In contrast to vitamin K1, vitamin K2 can have differently sized terpene side chains. Vitamin K1 is mainly assimilated with vegetable food, while vitamin K2 is formed by intestinal bacteria such as Escherichia coli. Hence, vitamin K deficiencies will appear, if an antibiotics treatment has affected the intestinal flora or it has not yet been formed as e.g. in newborns. 

Vitamin K is a blood coagulation factor and, among others, supports the steady flow characteristics of the blood. Vitamin K deficiencies slow down blood coagulation and can be responsible for increased bleedings after injuries. Also, the disposition to form hematomas, purpura, nose bleeding as well as gastrointestinal or mucous tissue bleedings can be caused by vitamin K deficiency.