Everything I was told about skincare oils starting out turned out to be wrong. They don’t seal in skincare - or moisture - very well. My dry skin needed more than just oil. And rosehip seed oil? Definitely not replacing my prescription retinoid. 

I had to scrap everything I thought I knew and start over. Luckily, you don’t have to. This guide breaks down the science of facial oils - their structure, how they work, what they actually do for your skin, and everything I wish I had known. 

What are Facial Oils, Exactly?

Let’s delve into the more complex science for just a second - hang in there with me.

Fats and oils belong to a group of organic compounds called lipids, which are hydrophobic (insoluble in water). They consist of long chains of hydrocarbons (carbon and hydrogen atoms) and serve essential roles in the body, from transporting fat-soluble vitamins to energy storage and organ protection.

Here’s a quick breakdown of lipid types:

• Oils are triglycerides, meaning they consist of a glycerol molecule bound to three fatty acid chains. 

• Fats are also triglycerides, but remain solid at room temperature (~77°F). Example: shea butter.

• Steroids have a more complex ring structure. Cholesterol is one example used in skincare, while other steroids include hormones estrogen and cortisol.

• Waxes consist of two long chains bound together, making them esters rather than triglycerides. They contain a fatty acid and a long-chain alcohol, forming protective barriers.

• Membrane lipids play structural and signaling roles within cells. Phospholipids form the cell membrane with a water-loving phosphate “head” and two oil-loving “tails,” while glycolipids include a sugar molecule for cellular communication.

Now, let’s zero in on triglycerides, the key component of most facial oils.

Triglycerides: Saturated vs. Unsaturated

Triglycerides can be classified as fats or oils based on their melting point, which is determined by their fatty acid composition:

• Saturated fatty acids have single bonds between carbon atoms, allowing them to pack tightly together in a straight line, making them solid at room temperature.

• Unsaturated fatty acids contain one or more double bonds, introducing kinks that prevent tight packing, making them liquid at room temperature.

Now that we’ve covered the basics, let’s explore how facial oils benefit the skin - and where they fall short.

How Oils Benefit Our Skin (and how they don't)

So why do we add oils to skincare? Their primary role is as emollients - ingredients that smooth and soften the skin by filling gaps between dead skin cells. They lubricate the skin immediately and, over time, improve barrier function, flexibility, and water retention.

They provide an enjoyable experience to consumers as they make the skin feel smooth and add a transient glow. They also serve other functions such as:

• Solvents for other oily ingredients like retinol or fragrance.

• Standalone vehicles - deliver those oil-soluble ingredients to the skin.

• Moisturizer components – contribute to the oil phase in emulsions and act as emollients.

What Oils Don’t Do

1. Most oils are not occlusive - meaning they don’t create a waterproof seal to trap hydration.

2. Oils aren’t replacements for actives – they’re supporting players, not the star ingredient.

Why Aren’t Oils Occlusive?

It all comes down to structure. Since plant oils are made up of mainly unsaturated triglycerides with varying fatty acid chain lengths and kinks, they struggle to form the tight, uniform barrier needed for occlusion3.

Compare this to hydrocarbons like petrolatum which contain only hydrogen and carbon. It’s a little like a game of Tetris, where straight pieces are easier to fit together without gaps. Mineral oil has straight hydrocarbon chains but they vary in length, making it slightly less occlusive than petrolatum.

Properties of an Effective Occlusive

1. Remain on the skin surface (substantive)

2. Form a tight, waterproof seal

Plant oils typically have structural components that allow them to penetrate the skin, where hydrocarbons lack these functional groups2. But remember, occlusivity is a scale and we see varying levels of occlusion depending on the ingredient and concentration. Some oils with saturated fatty acids (like babassu oil) should provide some occlusion as do fats.

How To Use Facial Oils the Right Way

Since most oils don’t seal in skincare, we need to rethink traditional layering advice. Here’s how to use facial oils effectively:

#1 Mix Into Your Moisturizer

If you don’t know whether your oil is occlusive or not (or all this info is making your head spin), the easiest option is to mix a few drops into your moisturizer. Works for all oils and amazing for skin needing extra TLC.

#2 Apply Before Moisturizer

Emollient oils can be applied before a moisturizer that contains occlusives. This is also ideal for oil serums with actives like bisabolol, retinol, or tetrahexyldecyl ascorbate.

#3 Use As Your Moisturizer

Most moisturizers are emulsions that utilize a combination of ingredients but there’s no rule that says you can’t just use your facial oil - if that’s enough for your skin.

Tip: for best with this method, apply a hydrating toner or serum first and then go in with a facial oil blend that offers a little occlusion like squalane. Stratia Skin’s Aqua Factory with Fortify on top is the perfect example. 

#4 Buffer Irritating Actives

Applying a barrier-supporting oil (like Fortify again) before tretinoin or other topicals with irritation potential can reduce irritation without blocking efficacy - unlike petrolatum, which could interfere with penetration.

Choosing The Best Facial Oil For Your Skin Type

Before purchasing a facial oil, it’s a good idea to ask yourself: Do I need one?

Your moisturizer already contains emollients, which may be enough. Stratia Skin Liquid Gold has a number of oils that work together with the other lipids.

Add a standalone oil if: your moisturizer just isn’t cutting it, mature or dry skin lacking lipids. or you just want to.

Common Ingredients in Skincare Oils

• Plant oils & butters -  fatty acid profiles determine their properties

• Esters -  lightweight and fast-absorbing alternatives to oils.

• Hydrocarbons (e.g., squalane) - more occlusive than oils.

• Oil-soluble actives - bisabolol, retinol, Vitamin C derivatives, Vitamin E.

Facial Oils by Texture

• Light or Dry Finish: Grape seed oil, hemi-squalane*, rosehip seed oil, most fruit seed oils.

• Medium Weight: Argan oil, sea buckthorn oil, pumpkin seed oil, jojoba oil, sunflower seed oil.

• Rich or Occlusive: Squalane*, mineral oil*, avocado oil, macadamia oil, marula oil.

(*Not an oil, but commonly used in facial oils.)

Do Oils Offer Benefits Beyond Emollience?

It’s important to understand that many components of oils - like fatty acids - are either in small quantities or bound. Seeing them listed in an oil doesn’t mean they’ll act on the skin. There are oils with some free antioxidants present, making them a nice addition alongside a dedicated antioxidant serum.

• Antioxidant-Rich Oils: Sea buckthorn oil, most fruit seed oils, rosehip seed oil.

Debunking the Most Popular Myths

“Rosehip oil is a great source of Vitamin A and Vitamin C, use it for scars and wrinkles.”

False. While rosehip oil contains all-trans retinoic acid, the levels are far too low to have a therapeutic effect. And while fresh rosehips contain Vitamin C, this water soluble vitamin is unlikely to be in the oil. Reported benefits likely come from its emollient properties.

“Oils should be applied last to seal in your skincare.”

False. Most oils aren’t very occlusive, as discussed.

“Dry skin needs oil.”

Partially true. Dry skin has depleted or disorganized skin lipids due to several factors. Oils help with dryness over time by supporting the skin barrier and immediately smooth roughness and flakes. But dehydration is a huge component of dry skin and requires occlusives and humectants too.

“Oils are beneficial for the skin because they’re rich in fatty acids.”

Unclear.

Linoleic acid (LA) is one of the most recommended fatty acids for the skin, while oleic acid (OA) is rarely used alone due to potential barrier disruption. However, fatty acids in oils are bound in triglycerides and must be hydrolyzed into free fatty acids (FFAs) to become bioavailable.

Our skin has lipase enzymes that assist with this5, but they’re primarily concentrated in hair follicles and limited in number. Plant oils naturally contain some FFAs, which increase with UV exposure, moisture, and heat - but since FFAs are unstable, this can mean they’re going rancid.

Research on this topic is limited. Some studies suggest LA-rich oils applied to acne-prone skin may increase LA in sebum, restoring its normal ratio. Compared to high-OA oils, which can disrupt the barrier, these oils appear to preserve barrier function - though whether fatty acids are responsible remains unclear. Small sample sizes and lack of replication make these findings uncertain.

After researching the topic, I came across an excellent deep dive from Dr. Michelle Wong of Lab Muffin Beauty Science that goes even further. In her video, Skincare Oils and Fatty Acids: The Science, Dr. Wong utilizes her PhD in medicinal chemistry to examine whether bound fatty acids can be utilized by the skin - a must watch that raises some important points.

The Takeaway

Oils are excellent emollients, leaving skin soft and supple while supporting the skin barrier. There’s no such thing as “just emollients” either - their use has been linked to improved skin disorders, faster repair, and better overall skin health.

Despite popular belief, oils aren’t the best for sealing in skincare. Instead, layer them under moisturizer or mix them in for a boost. While other components within oils (like antioxidants) shouldn’t be relied on alone, they’re a nice bonus.

On the hunt for an oil? Stratia’s Fortify hits all the benefits we covered. Thanks for reading!

References

1. Barnes, T. M., Mijaljica, D., Townley, J. P., Spada, F., & Harrison, I. P. (2021). Vehicles for drug delivery and cosmetic moisturizers: Review and comparison. Pharmaceutics, 13(12), 2012. https://doi.org/10.3390/pharmaceutics13122012

2. Barry, B. W. (2001). Lipids and skin: Permeability and occlusion. European Journal of Lipid Science and Technology, 103(12), 783–797.

3. Baumann, L. (2015). Chapter 8: Occlusives. In Cosmeceuticals and cosmetic ingredients. McGraw-Hill Education. https://dermatology.mhmedical.com/content.aspx?bookid=2812&sectionid=24497802

4. Belsito, D. V., & Fowler, J. F. (2012). Safety assessment of cosmetic ingredients: Emollients and occlusives. Dermatologic Therapy, 25(6), 387–394. https://doi.org/10.1111/j.1525-1470.2012.01865.x

5. Jimenez-Acosta, F., Planas, L., & Penneys, N. S. (1990). Lipase expression in human skin. Journal of Dermatological Science, 1(3), 195–200. https://doi.org/10.1016/0923-1811(90)90131-v

6. LibreTexts. (2022, September 15). Fats and Oils. In The Basics of GOB Chemistry (Ball et al.). Chemistry LibreTexts. https://chem.libretexts.org/Bookshelves/Introductory_Chemistry/Basics_of_General_Organic_and_Biological_Chemistry_(Ball_et_al.)/17%3A_Lipids/17.02%3A_Fats_and_Oil

7. LibreTexts. (n.d.). Lipids. In General Biology 1e (OpenStax). Biology LibreTexts. https://bio.libretexts.org/Bookshelves/Introductory_and_General_Biology/General_Biology_1e_(OpenStax)/1%3A_The_Chemistry_of_Life/3%3A_Biological_Macromolecules/3.3%3A_Lipids

8. Purnamawati, S., Indrastuti, N., Danarti, R., & Saefudin, T. (2018). The role of moisturizers in addressing various kinds of dermatitis: A review. Clinical Medicine and Research, 16(1-2), 31-38. https://doi.org/10.3121/cmr.2018.1370

9. Viljoen, J. M., Cowley, A., du Preez, J., Gerber, M., & du Plessis, J. (2015). Penetration enhancing effects of selected natural oils utilized in topical dosage forms. Drug Development and Industrial Pharmacy, 41(12), 2045–2054. https://doi.org/10.3109/03639045.2015.1047

10.  Zouboulis, C. C., et al. (2014). Topical treatment of facial acne with oils rich in linoleic acid. Dermato-Endocrinology, 6(1).

Mira is a skincare educator, blogger, and the content creator behind Skin Science by Mira and The Skincare Forum on Facebook. While skincare keeps her busy, she’s also pursuing her degree in Nursing and loves to spend her free time hiking.  As a content writer for Stratia Skin, Mira shares her evidence-based approach to skincare topics and a passion for making science accessible.