Many of the water-soluble ingredients are moisturizers (hygroscopic agents). The main reason for their moisturizing is that they have hydroxyl groups (OH), which can be combined with water (holding water molecules), such as various alcohols and polysaccharide moisturizers.
The new moisturizing concept is to help start aquaporin, such as urea. The following are common, water soluble moisture absorbents:
Glycerin: Glycerol, with three hydroxyl groups, is the benchmark for the measurement of moisturizing effect, cheap and easy to use
Propylene glycol: has two hydroxyl groups, good moisture retention but not as sticky as glycerin, may have some irritation at high concentration
1,3-butanediol: moisturizing, antibacterial, non-sticky, can also be used as a solvent for flavors and pigments
Polyethylene glycol: relative molecular weight is 200-2000, different molecular weights will have different texture
Sorbitol: good moisturizing, comparable to glycerin, with sweetness, excellent moisturizer
Lactic acid and sodium lactate: a component of the skin's natural moisturizing factor (NMF) that retains moisture levels over glycerin and regulates skin pH. However, the polarity is strong and it is difficult to match.
Sodium pyrrolidincarboxylate (sodium PCA): a composition of NMF that is more hygroscopic than glycerin and has no irritation and is an excellent moisturizer. PCA sodium has excellent skin feel, moisturizing but no sticky feeling
Sodium hyaluronate: the so-called "hyaluronic acid", star moisturizing ingredients
Aloe Vera: extracted from aloe vera leaf, the main ingredient is aloe polysaccharide, moisturizing, anti-inflammatory, and has certain antibacterial properties, promoting repair
Silk peptide: the formation of silk hydrolysate, the anti-corrosion of raw material processing is more difficult to handle, no stimulation
Others include trehalose, white fungus extract, etc.