Lactose
Properties
| State | Solid (white crystalline powder) |
| Color | White |
| Solubility | Soluble in water (195 g/L at 25°C); insoluble in ethanol |
| Melting Point | 202.8°C (anhydrous) |
| Boiling Point | Decomposes before boiling |
About Lactose
Lactose is a disaccharide made of one D-galactose joined to one D-glucose through a beta-1,4-glycosidic bond — the same molecular formula as sucrose and maltose (all C12H22O11) but a completely different sugar functionally. It's the only carbohydrate of any consequence in mammalian milk: human breast milk runs about 7% lactose by weight, cow's milk about 4.7%, and goat's milk closer to 4.1%. Hydrolysis to glucose + galactose requires the brush-border enzyme lactase (beta-galactosidase, encoded by LCT). Most adults globally — roughly 65-70% — downregulate lactase production after weaning, a state called lactase non-persistence. Persistence into adulthood is a relatively recent (about 7,500-10,000 years old) evolutionary adaptation found mainly in populations descended from Neolithic dairying cultures: Northern Europeans, certain East African pastoralists like the Maasai, and parts of the Middle East. In pharmaceuticals, lactose is hands-down the most-used tablet excipient on the planet — direct-compression alpha-lactose monohydrate flows well, compresses without lubricant, and is chemically inert with most APIs. Aerosolized fine-grade lactose is also the carrier in the dry-powder inhalers used for asthma (Advair, Spiriva). Lactose is a reducing sugar — the glucose unit's anomeric carbon is free — so it gives a positive Benedict's, Fehling's, and Tollens' test, distinguishing it from sucrose, which is non-reducing.
Where you'll encounter it
If you've ever swallowed a generic ibuprofen tablet, used an asthma inhaler, or watched someone with lactose intolerance regret a slice of pizza, you've encountered lactose. Open any over-the-counter drug bottle and read the inactive ingredients — alpha-lactose monohydrate is right there in roughly 60% of oral solid-dose pharmaceuticals because it flows through high-speed tablet presses at 300,000 tablets per hour without binders or lubricants. The Advair and Spiriva inhalers used by asthma and COPD patients use micronized lactose as the carrier powder that drags the active drug particles into the lungs on inhalation. And in dairy chemistry, the slow Maillard reaction between lactose and milk proteins is what gives evaporated milk its caramel undertone and turns infant biscuits golden brown during baking.
Common Uses
- Direct-compression filler in roughly 60% of all oral solid-dose pharmaceuticals
- Carrier for inhaled steroids and bronchodilators in dry-powder inhalers
- Infant-formula primary carbohydrate at ~7% w/v matching breast milk
- Bacterial growth substrate in MacConkey agar and the lac operon in E. coli
- Maillard browning agent in cheese-cracker and infant biscuit baking
- Substrate for industrial lactase production of glucose-galactose syrup
- Crystallization seed in evaporated milk and ice-cream texture control
Safety Information
GRAS for food use, no GHS hazard classification, no OSHA PEL. Causes osmotic diarrhea, bloating, and flatulence in lactose-intolerant individuals at doses above 12-15 g (roughly the lactose in one cup of milk). Dust inhalation in pharma manufacturing is a nuisance dust hazard — ACGIH TWA 10 mg/m3 (total) and 5 mg/m3 (respirable). Galactosemia patients (rare congenital disorder, lacking GALT) must avoid lactose entirely from infancy because galactose accumulation causes liver damage, cataracts, and intellectual disability.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.