According to the strength of action
(1) solvent with small surface tension and miscible with water, including ethanol, propylene glycol, glycerin, two methyl sulfoxide, etc..
(2) surfactants, such as anionic surfactants, certain polyols, surfactants (Pan, Twain), polyoxyethylene surfactants.
According to the route of administration
(1) wetting agents used in topical preparations, including surfactants and alcohols with little surface tension and miscible with water.
(2) the wetting agents used in oral preparations include small amounts of ethanol, glycerin, Twain, etc., which have little surface tension and can be miscible with water.
(3) injection of wetting agents, including small surface tension, and can be miscible with water ethanol, propylene glycol, glycerin, polyethylene glycol, 200~400, and Twain -80. 
according to the nature
Wetting agents have anionic and nonionic surfactants.
Anionic surfactants include alkyl sulfates, sulfonates, fatty acids or fatty acid esters, sulfates, carboxylic acids, soaps, phosphates, etc..
Nonionic surfactants include polyoxyethylene alkyl phenol ether, polyoxyethylene fatty alcohol ether, polyoxyethylene PEO block copolymer, etc..
Currently on the market there is a class of new silicon alcohol nonionic surfactant, also known as wetting agent, features: low molecular weight, more hydrophobic umbrella shaped symmetrical structure, compared with traditional surfactants, wetting and penetration performance is very excellent, efficient, is a new generation of surfactants revolutionary. The dynamic and static surface tension is very low, and it contains double hydroxyl group. The reactive agent is inert chemically and generally does not participate in the chemical reaction of the system. It has good acid and alkali resistance and chemical stability. Typical models are: GSK-588/582/585 and other series.