Beyond emollients: A review of moisturizers in dermatology

INTRODUCTION

The integrity of the epidermal barrier is central to cutaneous homeostasis and overall skin health. Disruption of the stratum corneum barrier is a common pathogenic denominator in several dermatological conditions. Restoration and maintenance of this barrier is a fundamental therapeutic goal in dermatology practice. Moisturizers, once regarded primarily as cosmetic agents, are now recognized as an essential therapy component. It plays a vital role in skin hydration, softness, and overall skin health. Over the past two decades, moisturizer formulations have evolved considerably, incorporating physiologic lipids, ceramides, natural moisturizing factors (NMFs), and novel delivery systems aimed at mimicking or restoring normal barrier architecture. With countless options available today, choosing the right moisturizer can be overwhelming.

Despite the widespread use of moisturizers, the existing literature remains fragmented, often limited to disease-specific applications. There is a scarcity of comprehensive, clinically oriented reviews that integrate formulation science with evidence-based practice. This article begins by reviewing the role of moisturizers in skin barrier maintenance, and then it discusses the type of moisturizers and their dispensing formulations, the choice of moisturizers to be used, the method of application, and therapeutic moisturizers. It also mentions the newer additives to moisturizer components while explaining the adverse effects moisturizers can cause. This review aims to comprehend current knowledge on moisturizers and to provide a rational framework for their use in everyday dermatology.

ROLE OF MOISTURIZER IN SKIN BARRIER MAINTENANCE

Among the many functions of the skin, one important function is the barrier function, the failure of which leads to increased transepidermal water loss and various dermatitis.

Stratum corneum is an active membrane explained by the Brick and Mortar model [Figure 1], where stratum corneum corneocytes with a resistant envelope and keratin microfibrils are the bricks, while the layers of lipid between the cells are the mortar.^[1] The main barrier to water loss is the lipid mortar. A key difference between the current and the earliest version of the model is the understanding that the bricks are now known to be connected by desmosomes. Desmosomes are glycoproteins that connect corneocytes. Corneodesmosin is an additional protein in the desmosomes joining stratum corneum corneocytes when compared to other keratinocytes of the epidermis.^[2] Thus, they are sometimes referred to as corneodesmosomes.

Close

Figure 1:

A “Bricks and Mortar” model for human stratum corneum illustrating the corneocyte “Bricks,” the Intercellular lipid “Mortar,” and the desmosomes connecting the corneocytes.

Export to PPT

The lamellar bodies formed at the stratum granulosum contain lipids, which are released to the intercellular space as the stratum corneum forms. These lipids essentially contain ceramides, cholesterol, cholesterol esters, and long-chain fatty acids. These lipids form the mortar and are critical for the barrier function of the skin.

Water from the deeper epidermal layers moves upward to hydrate stratum corneum cells and is then lost to evaporation. The pivotal factor in skin water flux, retention, and overall moisturizing level is the structure of the stratum corneum. There are four key processes in stratum corneum formation and functioning: corneocyte, stratum corneum lipid, NMF, and desquamation.^[3] Corneocytes are the physical barrier of the stratum corneum, contributing to elasticity when hydrated. The lipid bilayer is the mechanical barrier, allowing entry of most topically applied medications despite preventing many chemical entries. The NMF is a mix of hygroscopic molecules maintaining corneocyte hydration. In desquamation, corneodesmosomes are degraded by water-dependent hydrolytic agents, which work less efficiently in the low-moisture stratum corneum. Thus, lessened moisture content leads to the accumulation of corneocytes, and dry skin appears.^[4,5] Stated more simply, dry skin occurrence is due to^[6] (i) abnormalities of intercellular lipids of the stratum corneum, (ii) lack of NMFs, and (iii) abnormal desquamation of the stratum corneum.

Moisturizers suppress moisture loss from the stratum corneum and supply moisture to the dry skin after application. The skin barrier restoration through moisturizers works in a four-step process: ^[6] (1) the oily component of the moisturizer creates a thin film on the skin, and barrier repair begins; (2) the skin moisture distribution coefficient changes; (3) moisture diffuses from the dermis to the epidermis; (4) water distribution to the epidermis is controlled by the synthesis of skin lipids and intercellular lipid secretion. That is, the oily component of the moisturizer forms a film on the skin to prevent the evaporation of moisture, the humectant component directly supplies moisture to the epidermis and dermis, and the emollient component controls the exfoliation of dead skin cells to restore the skin barrier.^[6] In addition, when components similar to lipids in the stratum corneum of the skin are included in the moisturizer, the lipid component is supplied to the keratinocytes of the epidermis to rearrange the intercellular lipids, thereby maintaining the moisture content in the epidermis and improving the function of the skin barrier.^[7,8]

Thus, moisturizers increase stratum corneum water content and improve skin hydration; they smooth skin surface by filling the spaces between the partially desquamated skin and restore the ability of stratum corneum intercellular lipids to absorb, retain, and redistribute water. They also cause the degradation of corneodesmosomes and prevent the accumulation of corneocytes.^[5]

TYPES OF MOISTURIZERS AND THEIR DISPENSING FORMULATIONS

Moisturizers can be emollients, humectants, occlusives, and protein rejuvenators [Table 1].^[5,6]

Emollients are substances that primarily focus on softening and smoothing the skin by filling gaps between skin cells with lipids, which contain fat. This action helps to improve the skin’s texture, elasticity, and reduce roughness and flaking without altering the transepidermal water loss (TEWL).^[9]

Humectants are hydrophilic substances that attract and bind water from the dermis into the stratum corneum or from the environment under humid conditions. They maintain skin hydration by increasing water content in the outer skin layers, but require an occlusive or adequate ambient humidity to prevent net water loss.^[9,10] Occlusives are hydrophobic agents that form a barrier over the skin surface to inhibit TEWL by creating a physical film, thus sealing moisture within the stratum corneum. They are most effective when applied over damp skin or combined with humectants.^[9]

Protein rejuvenators are agents that aim to restore or mimic the protein structure and function of skin’s NMFs or structural proteins such as keratin and filaggrin. They may enhance hydration, improve elasticity, and aid in the repair of the epidermal barrier by replenishing amino acids or polypeptides lost in dry or damaged skin.^[10]

Depending on the dispensing medium, moisturizers can be of different formulations. Emulsifiers stabilize moisturizers. Cosmetic emulsion is the predominant form of delivery, while a kinetically stabilized colloidal suspension of immiscible liquids is the other form.^[11] There is no discernible phase distinction between the two phases. Water is the most essential and commonly used raw material in moisturizer formulations. The moisturizer category and its formulation characteristics are given in Table 2.^[10-12]

CHOICE OF MOISTURISER

When choosing a formulation, skin type is the most critical factor (dry, oily, normal, and combination are the selection criteria). For dry skin, select an ointment or oily cream formulation, and for oily skin, choose a lotion- and water-based cream formulation.^[6] The body part to be used is also a consideration. For hands, feet, shins, and lips, which are prone to dry skin due to their small number of sebaceous glands, an ointment or cream formulation containing a large amount of occlusive agents should be selected.^[5] In fact, it is less preferred to use ointments while lotion, gel, and serum formulations are more preferred.^[12] Powder and suspension forms of moisturizers are better used in intertriginous areas.^[10] In addition, it is preferable to use a moisturizer-oriented product in summer and an oil-based cream formulation containing large amounts of occlusive agents in winter.^[6] The choice of moisturizer also necessitates the consideration of its contraindications. It should be avoided in actively oozing lesions or clinically infected skin, as they delay healing and exacerbate infection. Acne-prone skin warrants the use of non-comedogenic, water-based lotion formulations to minimize follicular occlusion and thereby acne flare. Patients with sensitive skin syndrome benefit from hypoallergenic, fragrance-free preparations.

METHODS OF MOISTURIZER APPLICATION

The efficacy of moisturizers significantly depends on appropriate timing and technique. While humectants and hydrophilic formulations function by attracting moisture from the atmosphere or deeper skin layers, occlusive agents are best applied to damp skin immediately following bathing or showering. After warming the product between the palms, it should be gently applied in the direction of hair growth.

To minimize the risk of oil folliculitis caused by excessive friction, patients should receive clear instructions on proper application methods. The distribution of moisturizers is influenced by the formulation of the vehicle.^[5] High-viscosity ointments tend to provide more uniform coverage than lower-viscosity or volatile preparations. Transfer of active ingredients to external surfaces is more pronounced in creams and ointments compared to lotions or tinctures. Post-application, active compounds may remain on the skin, be absorbed, metabolized, or lost through evaporation, desquamation, or physical contact. Studies indicate that only about 50% of the moisturizer remains on the skin surface 8 h after application.^[5] Consequently, application frequency should be tailored to the severity of skin dryness, typically ranging from 1 to 3 times daily.

THERAPEUTIC USES OF MOISTURIZERS

Moisturizers are as important for routine skin care as they are for managing skin conditions with a weakened skin barrier or in cases of dry skin. The ideal moisturizer should have the wetting function of NMFs, the sealing function of the skin lipid membrane, and the barrier function of the lipid between keratinocytes.^[13] They serve a key supporting role in treating skin disorders such as atopic dermatitis, psoriasis, contact dermatitis, and other eczemas.

THE NEW ERA OF MOISTURIZERS

The modern use of moisturizers, apart from the traditional functions, targets dampening the immune response and restoring the microbial balance. Newer moisturizer contents include endocannabinoids, anti-inflammatory agents, antioxidants, bioactive lipids, and microbiome modulators.^[33] Cutaneous cannabinoid dysregulation leads to chronic inflammatory conditions of the skin, while endocannabinoids and bioactive lipids are increasingly being used in moisturizers for restoring skin homeostasis.^[34] They serve as a steroid-sparing alternative, mitigating itch and inflammation in eczematous dermatoses.^[33]

Recently, aloe vera (anti-inflammatory, anti-pruritic, analgesic, and wound healing properties^[35]), bisabolol (anti-inflammatory and antipruritic properties^[36]), shea butter (anti-inflammatory and anti-tumor promoting effects^[37]), and glycyrrhetinic acid (anti-inflammatory, antiviral and antitumor effects^[38]) are additions to moisturizer contents along with niacinamide and zinc gluconate to enhance the efficacy. Inflammatory dermatoses are associated with altered microbial composition of skin, and microbial restoration can be done using moisturizers.^[39]

Surface microbial restoration can be in the form of prebiotics, probiotics, parabiotics, and postbiotics, and are believed to increase regulatory T-cell response with subsequent suppression of Th2 and Th17- mediated immune responses.^[40] Lactobacillus brevis or Lactobacillus sake containing moisturizers resulted in decreased TEWL, xerosis, and pruritus.^[41,42] Studies with Bifidobacterium longum lysate cream and Roseomonas mucosa solution have also reported reduced skin sensitivity and decreased severity of inflammatory dermatoses, and atopic dermatitis in particular.^[43] Thus, the shift from traditional moisturizers to those with newer inclusions opens a realm of possible therapeutic options for patients with barrier-defective cutaneous conditions.

ADVERSE EFFECTS OF MOISTURIZERS

Although moisturizers offer numerous benefits, they are not devoid of adverse effects. Skin irritation is the most common adverse effect, while allergic contact dermatitis, photocontact dermatitis, and occlusive folliculitis are a few others. The adverse effects of moisturizers with their plausible causes are listed in Table 3.^[44]

CONCLUSION

Moisturizers play a vital role in maintaining skin hydration, enhancing barrier function, and improving overall skin health. With a wide range of formulations tailored to different skin types and conditions, they offer substantial benefits in both cosmetic and therapeutic contexts but are not exempt from risks. Optimal moisturizer selection based on individual needs and ingredient compatibility is essential for maximizing benefits and minimizing adverse effects. Despite their widespread prescription, evidence remains heterogeneous with limited comparative and long-term clinical data. Future studies addressing formulation-specific efficacy and standardized outcomes are needed to enable more precise recommendations.