Raw Material Spotlight: Humectants, Emollients & Occlusives – Key Ingredients for Skin Hydration

In our December 2024 newsletter, we explored the differences between dehydrated and dry skin—one rooted in a lack of water and the other in a deficiency of oils and barrier function. Understanding this distinction is vital, but knowing how to address each issue requires a deeper dive into the raw materials used in skincare formulations.

We are starting off 2025 by focusing on the three key categories of moisturizing ingredients: Humectants, Emollients, and Occlusives. For cosmetic chemists, understanding these materials is not just about identifying their benefits—it's about knowing their mechanisms, their best uses, and their real-world applications.

Let’s break it down, starting with the skin's natural moisture regulator: Transepidermal Water Loss (TEWL).

Transepidermal Water Loss (TEWL): The Gatekeeper of Skin Hydration

TEWL refers to the evaporation of water from the skin's surface into the environment. It’s a natural, passive process, but when disrupted, it can lead to dryness, irritation, inflammation, and a weakened skin barrier (Kang et al., 2022).

At the heart of TEWL regulation lies the stratum corneum, the outermost layer of the skin. This layer functions as a brick-and-mortar structure, with corneocytes (bricks) embedded in a lipid matrix (mortar) made of ceramides, cholesterol, and fatty acids (Harvard Health Publishing, 2019).

When this structure is disrupted—whether by harsh soaps, cold weather, or over-exfoliation—water escapes more rapidly, leaving the skin dry and vulnerable (American Academy of Dermatology Association, 2023).

In skincare, minimizing TEWL is a primary goal of moisturizers, which typically combine humectants, emollients, and occlusives to maintain optimal hydration levels.

Humectants: Attracting and Retaining Moisture

What Are Humectants?

Humectants are hygroscopic substances that draw water into the stratum corneum either from the deeper dermal layers or, in humid conditions, from the environment (Kang et al., 2022).

They function like tiny water magnets, binding moisture to the skin and improving hydration. Humectants are particularly effective in leave-on products like serums and creams, where prolonged contact allows them to work effectively.

However, in low-humidity environments, humectants may pull water from the deeper layers of the skin, which can paradoxically result in increased dehydration if not paired with occlusive agents?

Examples of Popular Humectants in Skincare:

• Hyaluronic Acid: Capable of holding 1,000 times its weight in water, HA is one of the most popular humectants in both leave-on and rinse-off products (Kang et al., 2022).
• Glycerin: A time-tested humectant that penetrates deeply into the skin, promoting long-lasting hydration?
• Snail Mucin: Rich in glycoproteins, hyaluronic acid, and glycolic acid, snail mucin is currently a skincare superstar, prized for its intense hydration and healing properties (Kang et al., 2022).
• Sodium PCA: Naturally found in the skin's Natural Moisturizing Factor (NMF), Sodium PCA helps maintain hydration levels.
• Panthenol (Pro-Vitamin B5): Known for its soothing and hydrating properties, panthenol penetrates the stratum corneum, attracting and holding water while improving skin barrier function (Draelos, 2012).

Emollients: Smoothing and Softening the Skin Barrier

What Are Emollients?

Emollients are lipid-based compounds that fill in the spaces between corneocytes, creating a smoother and softer skin texture (Cleveland Clinic, 2023).

Unlike humectants, emollients do not attract water but instead condition and restore suppleness to the skin barrier. They are essential for reducing roughness and flakiness caused by chronic dryness or barrier disruption.

Emollients are particularly beneficial for sensitive or inflamed skin because of their ability to reduce irritation and improve barrier integrity (Harvard Health Publishing, 2019).

Examples of Effective Emollients in Skincare:

• Squalane: A lightweight, non-comedogenic oil that mimics the skin's natural lipids.
• Ceramides: Essential lipids that reinforce the skin's barrier and reduce moisture loss (American Academy of Dermatology Association, 2023).
• Fatty Acids (e.g., Linoleic Acid, Oleic Acid): Found in various plant oils, they repair the lipid barrier.
• Plant Oils (e.g., Evening Primrose Oil): Rich in gamma-linolenic acid (GLA), Evening Primrose Oil helps reduce inflammation, support skin elasticity, and improve overall skin hydration (Proksch, 2008).
• Shea Butter: Rich in fatty acids and vitamins, it acts as both an emollient and a mild occlusive.

Occlusives: Locking in Hydration

What Are Occlusives?

Occlusives are hydrophobic agents that create a physical barrier on the skin surface to prevent water loss through TEWL (FDA Title 21, 2022).

They are often heavier in texture and are best applied as a final step in a moisturizing routine. Occlusives are particularly valuable for individuals with extremely dry or damaged skin barriers, where they act as a protective shield.

Examples of Powerful Occlusives in Skincare:

• Petrolatum: The gold standard for occlusives, capable of reducing TEWL by up to 99% (FDA Title 21, 2022).
• Dimethicone: A silicone derivative that forms a breathable barrier without leaving a greasy residue.
• Beeswax: Natural and skin-friendly, beeswax provides excellent occlusion.
• Lanolin: Known for its water-trapping abilities, lanolin is ideal for very dry skin.
• Shea Butter: Functions as both an emollient and occlusive agent, sealing moisture effectively.

Why This Matters for Cosmetic Chemists

Every raw material has a specific role to play in hydration, and understanding how humectants, emollients, and occlusives interact with the skin is essential for effective ingredient selection.

While humectants draw moisture in, emollients soften and condition, and occlusives lock everything in place. Together, they create a comprehensive moisturizing system that addresses TEWL, maintains hydration, and supports a resilient skin barrier.

This article serves as a reference point for chemists to better understand their raw materials, enabling them to choose ingredients with confidence and precision.

References:

1. American Academy of Dermatology Association. “Dermatologists’ Top Tips for Relieving Dry Skin.” 2023.
2. Gomes, A. A., & Silva, S. L. (2022). Vehicles for drug delivery and cosmetic moisturizers: Review and comparison. ResearchGate.
3. Harvard Health Publishing. “Moisturizers: Do they work?” May 29, 2019.
4. FDA. “CFR - Code of Federal Regulations Title 21.” July 20, 2022.
5. Kang SY et al. “Moisturizer in Patients with Inflammatory Skin Diseases.” Medicina (Kaunas). 2022;58(7):888.
6. Cleveland Clinic. “Emollients.” 2023.
7. Loden M. “The clinical benefit of moisturizers.” Journal of the European Academy of Dermatology and Venereology. 2005;19(6):672-88.
8. Proksch E. “The role of emollients in the management of dry skin conditions.” Skin Pharmacology and Physiology. 2008;21(5):227-232.
9. Rawlings AV, Harding CR. “Moisturization and skin barrier function.” Dermatologic Therapy. 2004;17:43-48.
10. Draelos ZD. “Moisturizers: The science of addressing dry skin.” Cosmetic Dermatology. 2012.