Paula's Choice Pro Retinaldehyde Dual-Retinoid Treatment

Unlike other plant oils, jojoba wax doesn't easily penetrate skin. It mostly works in the uppermost layers as an emollient. This just means it forms a light barrier on the skin to help retain moisture.

Formulations with jojoba esters up to 90% reduced transepidermal water loss (TEWL) and increased barrier recovery by 81% (outperforming bisabolol at 47%).

Besides barrier support, the science also suggests jojoba to have anti-inflammatory effects and potential applications for skin infections, aging, and wound healing.

Fun fact: Indigenous cultures have used jojoba as a moisturizer and to help treat burns for centuries.

Due to its fatty acid content, Jojoba oil may not be fungal acne safe.

Dimethicone comes in different viscosities:

Depending on the viscosity, dimethicone has different properties.

Ingredients lists don't always show which type is used, so we recommend reaching out to the brand if you have questions about the viscosity.

This ingredient is unlikely to cause irritation because it does not get absorbed into skin. However, people with silicone allergies should be careful about using this ingredient.

Note: Dimethicone may contribute to pilling. This is because it is not oil or water soluble, so pilling may occur when layered with products. When mixed with heavy oils in a formula, the outcome is also quite greasy.

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.

This ingredient may not be fungal acne safe because research has shown that the Malassezia species can grow in the presence of fatty acid esters with chain lengths above C12 (and this one is C18).

While it does have a comedogenic rating of 4, the comedogenic rating scale was developed from rabbit ear models which has limited clinical relevance to human skin. Studies also show that comedogenic ingredients cannot predict how the overall formula will behave on human skin.

This ingredient is biodegradable and commonly available in natural/COSMOS-certified grades.

Studies show retinal may work at a faster rate than retinol due to its structure.

All retinoids have to be converted into retinoic acid before starting to work. Some retinoids take several steps of conversion before binding. Retinal is only one step away, making it more potent.

Like other retinoids, retinal may be irritating. It is best to ease into using this ingredient frequently.

Using the 'ramp up' method, start by using retinol once a week. This gives your skin time to adjust and decrease irritation. Once you feel ready, you can slowly increase the frequency of retinol use.

Using retinoids will increase sun-sensitivity in the first few weeks of use. Though studies show retinoids increase your skin's natural SPF with continuous use, it is best to always wear sunscreen and sun-protection.

Another perk? It doesn't share the oxidative instability issues that vitamin A derivatives like retinol or retinaldehyde have.

One 12-week, double-blind, randomized trial found 0.5% OA was better at reducing wrinkle severity, comparable in improving pigment intensity, and was tolerated better than 0.5% retinol.

At 12 weeks, only 5% of the OA group reported burning and 10% reported scaling. The retinol group reported much higher rates of itching, burning, stinging, scaling, and redness.

Just remember this is a relatively new ingredient with limited long-term data; researchers noted the 12 week study's single trial site and short duration as limitations and recommended further studies with more diverse populations and longer timelines.

This ingredient is typically used at levels between 0.1% - 0.5%.

Topically applied tocopherol has been shown to protect against UV damage by ramping up the skin's own natural defense enzymes.

It also acts as a skin conditioning agent; some studies show that regular topical use can improve the skin's water-binding capacity over 2-4 weeks.

This ingredient is especially loved for being a team player. When combined with Vitamin C, the photoprotective effect of both ingredients roughly doubles and the combo also helps reduce UV-induced DNA damage.

This ingredient has some brightening potential but it's more of a prevention ingredient than spot-fader. Cell studies show it can slow down melanin production but it's worth noting that it's not the most powerful brightener out there.

In formulations, it also serves as a stabilizer that helps protect other oxidation-prone ingredients from degrading.

Concentrations usually range from 0.1-1% in most leave-on products.

Tocopheryl Acetate is commonly found in both skincare and dietary supplements.

Evidence-wise, its relatives (like Galactomyces) are the ones with the most published lab work. Keratinocyte studies show these ferments can boost barrier-related markers. This ingredient is generally assumed to behave similarly thanks to its overlapping composition.

This ingredient may not be fungal acne safe because its a fermentation filtrate. The exact composition is batch-variable and can include fatty acids and lipids byproducts.

This ingredient is typically used in concentrations between 1-10%. Studies have found it to be non-sensitizing, non-phototoxic, and non-photoallergenic.

A close cousin of this ingredient is Glyceryl Stearate SE ("self-emulsifying"). This just has a small amount of sodium or potassium stearate added so it can emulsify without a co-emulsifier.

Since this ingredient is an ester of a C18 fatty acid, it may not be fungal acne safe. The Malassezia yeast can potentially metabolize within the C11-C24 range.

Fun fact: The human body also creates Glyceryl Stearate naturally.

Fatty alcohols are usually derived from natural fats and oils and therefore do not have the same drying or irritating effect as solvent (ethanol) alcohols.

The FDA allows products labeled "alcohol-free" to have fatty alcohols.

This ingredient may not be fungal acne safe. It is a primary fatty alcohol with a chain length above 12 carbons. A study from 2019 show Malassezia can feed on fatty alcohols in this range, so it may trigger fungal acne in those prone to it.

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.

In skincare, it is an emollient that dries down to a solid film with water-binding properties. This helps keep skin hydrated and helps reduce transepidermal water loss (TEWL).

A 2026 dermatology review pulls together its broader uses:

Human clinical testing found this ingredient to be non-irritating and non-sensitizing.

Because castor oil contains fatty acids in the C11-24 range, this ingredient may not be fungal acne safe.

At this time, the literature does not support castor oil in regrowing hair. A 2022 systematic review found no strong evidence that it supports hair growth and only weak evidence that it improves hair shine.

Castor oil itself carries "perfuming" and "masking" function tags according to the official CosIng database. This is because of its mild odor and odor-dampening properties.

This ingredient is generally considered non-toxic, non-irritating, and has low absorption potential.

You might have heard that this ingredient clogs pores. This reputation comes from the older rabbit ear studies which are more sensitive than human skin to clogging.

Dermatologist Dr. Zoe Draelos has also confirmed in a peer-reviewed paper that products containing comedogenic ingredients are not necessarily comedogenic themselves.

A small subset of people (~2%) may experience contact sensitivity so patch testing is a reasonable idea if you have reactive skin.

Since this ingredient is an ester of myristic acid (a C14 fatty acid), it falls within the carbon chain range that is known to feed Malassezia. This ingredient may not be fungal acne safe.

This ingredient is not irritating or sensitizing. Recent research also suggests it may have skin-brightening effects through tyrosinase inhibition.

Caprylhydroxamic Acid is often used with natural antimicrobial products as an alternative to preservatives.

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.

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.

HSA is an emulsifier in certain formulations. Emulsifiers prevent ingredients from separating.

This ingredient may not be Malassezia folliculitis, or fungal acne, safe.

The skin's ability to produce ceramides gets disrupted in skin conditions like eczema. This in turn weakens the skin barrier and applying ceramides topically has been shown to replenish what's been lost to restore barrier function.

Most of the studies with Ceramide AP test it as part of a multi-ceramide complex; studies reinforce ceramide AP's role in rebalancing ceramides in skin and improving skin hydration.

Typical use levels in formulas range from 2-10%.

The CIR Expert Panel has concluded this ingredient to be safe as a cosmetic ingredient.

Since this ingredient is an ester of oleic acid, it may not be fungal acne safe. Oleic acid is a fatty acid that falls into the C11-24 range that Malassezia can metabolize.

However, this exfoliating effect only happens at high concentrations (20%) which can be hard to find in cosmetic products.

Due to this, citric acid is usually included in small amounts as a pH adjuster. This helps keep products slightly more acidic and compatible with skin's natural pH.

In skincare formulas, citric acid can:

While it can provide some skin benefits, research shows lactic acid and glycolic acid are generally more effective and less irritating exfoliants.

Most citric acid used in skincare today is made by fermenting sugars (usually from molasses). This synthetic version is identical to the natural citrus form but easier to stabilize and use in formulations.

Read more about some other popular AHA's here:

Titanium dioxide provides broad-spectrum protection mostly in the UVB and UVAII range, with some protection in the UVAI range.

While its UVA protection isn’t as strong as zinc oxide’s, the difference is minor.

A common myth is that mineral UV filters reflect UV light. However, modern research shows titanium dioxide absorbs UV radiation like chemical filters (~95% absorption & 5% reflection).

Thanks to its non-irritating nature, titanium dioxide is suitable for sensitive, acne-prone, or redness-prone skin. It is unlikely to cause "eye sting" like other sunscreen ingredients.

A major drawback of this ingredient is its white cast and thick texture. This is why mineral sunscreens often leave a white cast and are less cosmetically elegant than chemical/hybrid sunscreens.

To improve white cast and spreadability, micronized or nano-sized titanium dioxide is often used.

There are ongoing concerns surrounding nano-titanium oxide's impact on marine ecosystems.

There is no conclusive evidence that any form of titanium oxide (or any other sunscreen ingredients) will cause harm to marine ecosystems or coral reefs. The science is still developing but many consumers are keeping a close eye on this issue.

Please note, many destinations have reef-safety sunscreen rules. For instance, the U.S. Virgin Islands advises all visitors to use non-nano mineral sunscreens.

Nano mineral sunscreens once raised safety concerns about absorption into skin.

Extensive research has shown that they do not penetrate healthy or damaged skin; they remain safely on the surface and the top layer of dead skin (stratum corneum).

You'll likely find titanium dioxide bundled with alumina, silica, or dimethicone. These ingredients help make titanium dioxide highly photostable; this prevents it from interacting with other formula components under UV light.