Rare Beauty Hydrating Under Eye Patches

Dipropylene glycol is technically an alcohol, but it belongs to the glycol family (often considered part of the ‘good’ alcohols). This means it is hydrating and gentle on skin unlike drying solvent alcohols like denatured alcohol.

As a masking agent, Dipropylene Glycol can be used to cover the smell of other ingredients. However, it does not have a scent.

Studies show Dipropylene Glycol is considered safe to use in skincare.

It is also used to make a product more thick.

Xanthan gum is a pretty common and great ingredient. It is a natural, non-toxic, non-irritating ingredient that is also commonly used in food products.

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.

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%.

Tartaric acid is not as well studied as other AHAs, such as glycolic acid.

This ingredient is considered hypoallergenic and non-toxic. Cellulose Gum can be found in cosmetics, food, and other household goods such as paper products.

Typical use levels range from 10-20% in cleansers and 15-30% in shower products.

Once on your skin, your skin's glucoside hydrolases breaks it down into glucose and the parent fatty alcohols.

This ingredient is considered fungal acne safe because its fatty alcohol portion sits outside the Malassezia yeast's metabolization range.

Your skin has cells called fibroblasts that build collagen (the stuff that keeps skin firm and smooth). Adenosine basically flips a switch on these cells that tells them to get to work making more collagen and other proteins. These cells slow down on their own as skin ages, so Adenosine helps give them a little nudge to keep going.

The clinical backing is pretty solid too.

A blind, randomized, placebo-controlled trial of 126 women aged 45-65 tested a 0.1% cream twice daily and found real improvements in crow's feet and frown lines using a precise 3D skin-mapping technique; these changes showed up by week 3 and held at 2 months.

A later study using Adenosine-loaded dissolving microneedle patches reported gains in wrinkle depth, dermal density, elasticity, and hydration.

On concentrations, South Korea's Ministry of Food and Drug Safety has set 0.04% as the approved functional anti-wrinkle level. You'll typically see this ingredient used somewhere in the 0.04-0.1% range since it works at low doses.

This ingredient has been found safe for cosmetics with the data showing no irritation or sensitization.

Overall, this is a great ingredient for any anti-aging routine and has no photosensitizing effect, so it suits both AM and PM use.

Some studies suggest betaine may support making skin tone more even.

Fun fact: Betaine naturally exists in the skin and the body. In cosmetic products, it can be either plant-derived (most commonly from sugar beets) or synthetically produced for consistency and stability.

Betaine is also known as trimethylglycine.

Though this ingredient works well with most skin types, some people with sensitive skin may experience a reaction such as allergic rashes, closed comedones, or itchiness.

Lab studies demonstrate that some peptide fractions in this ingredient possess antioxidant and anti-collegenase effects, helping to protect the structural proteins in skin and soothing inflammation.

Additionally, this ingredient has been shown to have antimicrobial effects against bacteria associated with acne.

Early research also shows that caffeine can help calm redness, soothe irritated skin, and support hair growth by stimulating microcirculation in the scalp.

You might have seen eye creams marketing caffeine as a depuffing ingredient. This is because it is a vasoconstrictor meaning it can temporarily constrict blood vessels, though clinical evidence for this specific use is still limited.

Most skincare products contain this ingredient at concentrations between 1-6%. It is able to penetrate skin easily regardless of skin type or thickness.

Just so you know, a very small number of case reports describe caffeine-induced allergy. This ingredient is generally well-tolerated, non-irritating, and non-sensitizing for the majority of people.

On the safety side, the Cosmetic Ingredient Review Expert Panel has concluded this ingredient to be safe as used in current cosmetic practices + concentrations.

Typical use levels in a formula run about 1-5%.

These compounds allow centella to dial back inflammation, encourage the skin to build and hold onto collagen, support the barrier and hydration, and bring solid antioxidant activity to protect against signs of aging.

Centella also carries a nice supporting cast of Vitamin A, vitamin C, several B vitamins, and amino acids. Put it all together and you get an ingredient that soothes, hydrates, and protects, all at once.

Most of centella's magic comes from the four big compounds (Asiaticoside, Madecassoside, Asiatic Acid, and Madecassic Acid). These are the actives doing the heavy lifting in almost every centella study.

Here is the short version of what they do in the skin:

So it is not just soothing for the sake of soothing. Centella calms the skin AND helps it rebuild.

Just FYI, not all centella on an ingredient list is the same. What you are getting actually depends on the extract:

Fun fact on the ratios: the leaves tend to be richest in Madecassoside and Asiaticoside, and lower in the two acids. The exact amounts shift with where the plant is grown and how it is processed. This means purity really does vary brand to brand.

Centella is one of the most easygoing actives out there.

It layers well with basically everything: niacinamide, hyaluronic acid, peptides, and vitamin C, and also pairs nicely with stronger actives like retinoids and exfoliating acids where it can help take the edge off irritation.

On the safety side, centella and its triterpenes are classified as weak sensitizers, meaning allergic reactions are possible but uncommon.

Patch tests at 1% and 5% came back negative in test panels, and creams at typical use levels did not cause allergic reactions across large groups of people.

But as with any new active, a patch test is still a smart move for very reactive skin.

Centella is widely used because it is effective at low percentages. For context, human safety testing found no meaningful irritation from creams containing centella extract at everyday use levels (the tested amounts were well under 1%).

The irritancy threshold in animal testing was also above 30% (so real-world formulas sit far below anything concerning).

In collagen lab studies, higher concentrations drove more collagen synthesis, so serums built around centella tend to feature it more prominently.

Bottom line: you will find centella working nicely anywhere from a fraction of a percent up to hero-ingredient levels depending on whether it is a supporting soother or the main event.

Fun fact: Centella has been used as a medicine and in food for many centuries. As a medicine, it is used to treat burns, scratches, and wounds.

Either way, you're getting water + a cocktail of minerals and trace elements (like magnesium, calcium, potassium sodium, etc).

Officially, COSIng recognizes this ingredient as a humectant that holds and retains moisture, and solvent that helps dissolve other ingredients.

The claims about this ingredient come from its minerals. A 2025 systematic review found that seawater-based therapy showed moderate effectiveness at reducing atopic dermatitis severity and improving skin barrier function.

It also showed favorable safety profile and very minimal adverse effects.

The underlying studies pointed to improvements in stratum corneum hydration, lower transepidermal water loss (TEWL), and a healthier microbial balance.

Much of this benefit is actually attributed to magnesium: a 2005 study found that bathing in a magnesium-rich Dead sea salt solution improved skin barrier function, boosted hydration, and reduced inflammation in atopic dry skin.

It's worth nothing most of this evidence comes from bathing/soaking protocols and mineral-rich waters like the Dead Sea (not necessarily a few drops on an ingredient list).

Overall, this is a gentle, well-tolerated, water-phase ingredient that can offer light hydration and a little mineral boost.

The only caveat is that very high salt concentrations can be drying for already-dry skin.

Interestingly, the size of the molecule affects its behavior:

Some clinical evidence links low molecular weight versions to improved wrinkle depth, elasticity, anti-inflammatory effects, and barrier repair.

Many serums use a blend of both weights so you can get surface hydration plus longer-lasting and deeper effects.

You'll typically see concentrations between 0.1-2% for this ingredient.

Wolf's Bane has been said to have anti-inflammatory properties. However, studies are conflicting about whether this is true.

According to the Final report on the safety assessment of Arnica montana, this plant has not been found to cause dermal irritation.

This flower contains numerous fatty acids such as palmitic, linoleic, myristic, and linolenic acids. The presence and amount of fatty acids depends on where the flower is harvested.

Like other flowers, this ingredient has a natural fragrance. It can also be used to mask, or cover, the unpleasant scents from other ingredients.

Studies show green tea extract and its catechins (like epigallocatechin gallate (EGCG)) help your skin cells product energy more efficiently and reducing the number of free-radicals that can damage your skin from the inside.

In lab-grown skin models, this translated to younger, healthier, and stronger skin.

There's also good sun protection data; researchers saw less DNA damage and redness on human skin when green tea was applied before UVB exposure. And the more they applied, the better the protection.

Needless to say, this ingredient shouldn't replace your sunscreen. But it is a great supportive ingredient that you can already find in many sunscreens and antioxidant serums.

A 2009 study found a 2% green tea lotion was effective for mild-to-moderate acne thanks to its anti-inflammatory and mild antimicrobial activity.

The quality of the extract matters a lot here:

Good extracts contain 50-90% catechins while lower quality ones are mostly there for marketing. We recommend reaching out to the brand if you have questions about the quality or source of their ingredients.

Human Repeated Insult Patch Testing showed no irritation or sensitization at use concentrations (0.86% in leave-on products and up to 30% as leaf water).

Because it is not a free-fatty acid, this ingredient is fungal acne safe (there's nothing for Malassezia to feed on).

The comparison to Botox does have limits because the molecule is water-loving and relatively large.

Acetyl Hexapeptide-8 has a hard time absorbing deeply enough through the skin's outer barrier to actually reach the muscles.

So whether it truly works the way Botox does at a biological level is still up for debate, but early clinical outcomes are fairly encouraging.

A 12 week human study of a multi-ingredient regimen containing this ingredient saw:

While some studies have observed improvements in wrinkle appearance, it is important to note that more consistent results are seen in multi-ingredient formulations (vs just Acetyl Hexapeptide-8 alone).

Some research studies also used higher concentrations (up to 10%) while this ingredient is usually found in concentrations up to 0.005% in leave-on formulations.