Lactose is a sugar molecule, a disaccharide, soluble in water (hydrophilic) that divides into two other smaller molecules: glucose and galactose.

It is a sugar found in the milk of humans and pets and is of great importance as a basic nutrient.

In order for lactose to be absorbed from the intestine and into the body, it must first be broken down into glucose and galactose which are then absorbed by the cells lining the small intestine. The enzyme that breaks down lactose into glucose and galactose is found on the surface of the cells lining the small intestine.

What it is used for and where

Food

Lactose improves the metabolism of plasma lipids, especially triglycerides, and reduces the accumulation of hepatic cholesterol by maintaining a lower biliary cholesterol concentration; it also reduces the formation of gallstones, apparently through its impact on the metabolism of the large intestine (1).

Pharmaceutical Industry

 Lactose is a very common excipient, a dry powder binder in tablets because of its neutral taste, solubility and low cost characteristics. Many people are lactose intolerant and some pharmaceutical companies replace it with microcrystalline cellulose or cornstarch.  It is an excellent diluent with binding properties (it offers an excellent cohesion) and it is used for its ability to increase the degree of compactness in medicinal tablets. However it turns out to be decidedly incompatible with amine derivatives with formation of Schiff bases.

Cosmetics 

In the cosmetic industry there is a great interest in products synthesized from natural products for a reason of limited cost, availability, renewability. Sucrose, glucose, lactose have shown low toxicity and high biodegradability. Compounds derived from lactose have shown an excellent antagonistic activity against bacteria and fungi so that a wide range of cationic surfactants have been derived.

Agente condizionante della pelle - Umettante. Gli umettanti sono sostanze igroscopiche utilizzate per ridurre al minimo la perdita d'acqua nella pelle e per prevenirne l'essiccazione facilitando un più rapido e maggiore assorbimento di acqua nello strato corneo dell'epidermide.  L'epidermide è il più superficiale dei tre strati con cui è composta la pelle umana (epidermide, derma e ipoderma) ed è lo strato che provvede al mantenimento dell'idratazione in tutti e tre gli strati. A sua volta l'epidermide è composta da cinque strati: corneo, il più superficiale, granulare, spinoso, lucido, basale. Gli umettanti hanno la capacità di trattenere nello strato corneo l'acqua che attirano dall'aria ed hanno la funzione di idratare la pelle. Meglio utilizzarli prima degli emollienti che sono a base d'olio.

Safety

The digestive process of lactose in the human body needs a specialized enzyme, commonly called lactase. a β-galactosidase located on the upper surface of enterocytes on the microvilli of the small intestine. When an organism has a lactase deficiency, lactose cannot be absorbed and therefore is not properly digested (1).

Warning : it can cause intolerance

See "Lactose Studies"

Industrially it appears as a white, fine or crystalline powder.

Typical optimal characteristics of commercial Lactose product

• Molecular Formula: C₁₂H₂₂O₁₁
• Molecular Weight: 342.297 g/mol
• CAS: 63-42-3  5965-66-2
• EC Number: 200-559-2  227-751-9
• UNII: 13Q3A43E0S
• PubChem Substance ID 24896352
• MDL number MFCD00064521    MFCD00151251
• DSSTox Substance ID: DTXSID5058723
• PubChem Substance ID   329823055
• InChI=1S/C12H22O11/c13-1-3-5(15)6(16)9(19)12(22-3)23-10-4(2-14)21-11(20)8(18)7(10)17/h3-20H,1-2H2/t3-,4-,5+,6+,7-,8-,9-,10-,11-,12+/m1/s1 
• InChl Key      GUBGYTABKSRVRQ-DCSYEGIMSA-N
• SMILES    C(C1C(C(C(C(O1)OC2C(OC(C(C2O)O)O)CO)O)O)O)O
• IUPAC   (2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxane-3,4,5-triol
• ChEBI    36218
• Beilstein   93796

Synonyms: 

• Beta-Lactose
• beta-D-Lactose
• Fast-flo Lactose
• Pharmatose 450M
• Lactobiose
• beta-D-Glucopyranose, 4-O-beta-D-galactopyranosyl-
• (2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)oxan-3-yl]oxyoxane-3,4,5-triol
• Aletobiose
• (2R,3R,4S,5R,6S)-2-(hydroxymethyl)-6-[(2R,3S,4R,5R,6R)-4,5,6-trihydroxy-2-(hydroxymethyl)tetrahydropyran-3-yl]oxy-tetrahydropyran-3,4,5-triol
• Galactinum
• beta-D-Galp-(1->4)-beta-D-Glcp
• Tablettose
• Lactin
• 4-O-beta-D-Galactopyranosyl-beta-D-glucopyranose
• beta-D-Gal-(1-->4)-beta-D-Glc
• D-Lactose
• D-Glucose, 4-O-beta-D-galactopyranosyl
• Milk sugar
• beta-D-galactopyranosyl-(1->4)-beta-D-glucose
• Fast-flo
• (2R,3R,4R,5S,6R)-6-(hydroxymethyl)-5-((2S,3R,4S,5R,6R)-3,4,5-trihydroxy-6-(hydroxymethyl)tetrahydro-2H-pyran-2-yloxy)tetrahydro-2H-pyran-2,3,4-triol
• Lactose anhydrous

References________________________________________________________________________

(1) Hayes KC, Stephan ZF, Pronczuk A, Lindsey S, Verdon C. Lactose protects against estrogen-induced pigment gallstones in hamsters fed nutritionally adequate purified diets. J Nutr. 1989 Nov;119(11):1726-36. doi: 10.1093/jn/119.11.1726. 

(2) Fassio F, Facioni MS, Guagnini F. Lactose Maldigestion, Malabsorption, and Intolerance: A Comprehensive Review with a Focus on Current Management and Future Perspectives. Nutrients. 2018 Nov 1;10(11):1599. doi: 10.3390/nu10111599.