Lubricants
Water based
The default choice, compatible with every material and every barrier. The differences between formulas are larger than the category name suggests.
A water based lubricant is water thickened with a polymer, preserved so it does not grow anything in the bottle, and adjusted for acidity. That is the whole formula. The thickener decides the feel, the preservative decides the shelf life, and the dissolved content decides how the formula interacts with tissue.
Osmolality, in plain terms
Osmolality measures how concentrated a solution is compared with the fluid inside cells. A formula far more concentrated than the surrounding tissue draws water out of cells by osmosis, leaving the surface layer dehydrated and more fragile. Guidance from public health bodies has for years suggested keeping below roughly 1200 milliosmoles per kilogram, and a number of widely sold formulas sit far above that.
In practice, osmolality is rarely printed on a bottle. Two proxies help. Formulas built on large amounts of glycerine or propylene glycol tend to be concentrated. Formulas described as isotonic or body matched have usually been formulated with this in mind, and the maker will normally state the figure when asked.
Glycerine and glycols
Glycerine gives a slippery, slightly sweet feeling formula and holds water well. It is also a sugar alcohol, and for people prone to thrush it can contribute to recurrence. Propylene glycol serves a similar role and is a common contact irritant at higher concentrations. Neither is dangerous in the general sense; both are worth avoiding for anyone whose body has already objected once.
Preservatives and acidity
Every water based formula needs a preservative, since water plus thickener is a growth medium. Parabens are effective and unpopular; alternatives such as phenoxyethanol or sodium benzoate are common. Acidity matters too: vaginal tissue sits near pH 4, rectal tissue nearer pH 7, and a formula matched to the intended use is gentler than a single formula used everywhere.
Tackiness, and the fix
Water based formulas dry by evaporation and absorption, and the thickener left behind is what feels tacky. Adding more product makes a thicker layer of the same problem. A few drops of water reconstitute what is already there, which is why a small bottle of water beside the bed is more useful than a second bottle of lubricant.
Formulas differ widely in how long they last before that point. Thicker gels stay put and suit some uses; thin fluids feel more natural and need reapplication sooner. Ranges such as the inWonderstate listing publish the full ingredient list for each formula, which makes it possible to avoid a specific ingredient rather than guess.