Kate Somerville +Retinol Firming Eye Cream Versus Clinique All About Eyes Brightening Serum Concentrate

It does have a penetration-enhancing reputation that is a bit more nuanced than marketing suggests; a cell study on human skin found that 10% DMI didn't significantly boost the permeation of Hydroquinone, Salicylic Acid, or Octadecenedioic Acid compared to controls (though it did improve their solubility in the formula itself).

Typical usage concentrations usually range from 1-10% depending on the formula's needs; this ingredient is also well tolerated at these levels.

On top of that, this ingredient can counteract the effects of hard water by binding to the minerals in it.

One thing worth knowing is that Disodium EDTA has been shown to be a mild penetration enhancer. It can help other ingredients absorb into skin more effectively which can be a double-edged sword (great for actives, but can also make the active too strong if you have sensitive skin).

Clinical patch testing showed no significant skin irritation at typical use concentrations and minimal dermal absorption.

You'll most likely see this ingredient near the end of an ingredient list. It's typically found in concentrations less than 1%.

Your skin makes glycerin on its own (mostly from sebaceous oil breakdown) and shuttles it to your outermost layer of skin, or your epidermis, via aquaporin-3.

Aquaporin-3 is a transporter that is essential for normal skin hydration, elasticity, and repair. Interestingly, mice lacking in AQP3 have dry and less elastic skin that can be fully corrected with glycerin.

This ingredient is non-irritating, plays well with almost every ingredient, and works across all skin types. Typical use is anywhere between 3-10% but can go up to 79% in some leave-on products.

Just know very high concentrations (>40%) can feel tacky in low humidity.

Glycerin is the name for this ingredient in American English. British English uses Glycerol/Glycerine.

In practice, this means it does the classic retinoid jobs in a formula:

The best part is that it can do all this with noticeably less redness, flaking, and stinging than traditional retinoids.

That gentle reputation is backed by lab work as well; a 2018 study on skin models found that HPR triggered higher retinoid-gene activity than retinol, retinal, or retinyl propionate at the same concentrations while being less irritating to cells.

It also boosted procollagen production to levels similar to retinoic acid itself.

A 2023 study showed HPR works synergistically with retinyl propionate to switch on collagen-building pathways and a 2025 clinical serum study in women with mild photoaging saw improvements in wrinkles and elasticity (though that formula also contained retinol, peptides, and Silybin).

One naming quirk worth mentioning:

You'll likely see this ingredient sold under the trade name "Granactive Retinoid", which is actually only 10% HPR blended with 90% Dimethyl Isosorbide solvent. This means a 5% Granactive Retinoid really only means about 0.5% HPR.

Finished products typically land somewhere between 0.05-1% and it's happiest formulated at a mildly acidic to neutral pH (~5.5-6.5).

Another perk is that this is one of the more light- and temperature-stable retinoids which is a nice bonus for shelf life.

On a cellular level, it disrupts the cell membranes of microbes by poking holes that make the cell leak. This shuts down the chemical reactions the microbe needs to make energy so it can no longer survive.

Another perk of this ingredient is that it stays functional across a wide pH range (3-10).

You'll often see it paired with boosters like Ethylhexylglycerin; one study showed that a 1:9 ratio of Ethylhexylglycerin to Phenoxyethanol damages bacterial membranes as effectively as doubling the Phenoxyethanol concentration on its own.

Typical use concentrations range from 0.3-1% depending on the formula, and this ingredient is capped at 1% int the EU.

Safety-wise, the fear mongering does not hold up to the evidence. The EU's Scientific Committee on Consumer Safety and FDA consider it safe as a preservative at up to 1%, including for children of all ages.

Adverse systemic effects only showed up in animal studies at exposures roughly 200x higher than what people get from cosmetics. And despite its very widespread use, this ingredient is a rare sensitizer and allergic reactions are uncommon.

Propanediol is not likely to cause sensitivity and considered safe to use. It is derived from corn or petroleum with a clear color and no scent.

It is considered non-irritating on the skin.

You'll also recognize water as that liquid we all need to stay alive. If you see this, drink a glass of water. Remember to stay hydrated!