Moisturizers


Article Author:
Anne Harwood


Article Editor:
Karthik Krishnamurthy


Editors In Chief:
David Wood
Andrew Wilt
Hajira Basit


Managing Editors:
Avais Raja
Orawan Chaigasame
Khalid Alsayouri
Kyle Blair
Radia Jamil
Erin Hughes
Patrick Le
Anoosh Zafar Gondal
Saad Nazir
William Gossman
Hassam Zulfiqar
Navid Mahabadi
Hussain Sajjad
Steve Bhimji
Muhammad Hashmi
John Shell
Matthew Varacallo
Heba Mahdy
Ahmad Malik
Sarosh Vaqar
Mark Pellegrini
James Hughes
Beenish Sohail
Hajira Basit
Phillip Hynes
Sandeep Sekhon


Updated:
7/23/2019 10:31:03 AM

Introduction

To discuss moisturizers of the skin, we need a brief discussion on the structure and function of the skin barrier and of the mechanism of maintaining water balance.  The stratum corneum, the outermost layer of the epidermis, is the primary physiologic barrier of the skin and is of critical importance in maintaining water balance.[1]  The role of water within the stratum corneum is pivotal to the maintenance of normal skin integrity and turnover.[2] Water allows for increased flexibility of the tissues and is a crucial component of the enzymatic reactions responsible for cleavage of the corneodesmosomal connections between corneocytes during the desquamation process.  Below a critical water concentration, the corneodesmosomal connections remain intact, which results in a build-up of corneocytes and the appearance of dry, flaky skin.[3]

Function

The stratum corneum contains high concentrations of osmotically active molecules, including amino acids and their derivatives, lactic acid, urea, and electrolytes. These molecules form from the breakdown of filaggrin and are referred to as natural moisturizing factor (NMF). The molecules that make up NMF are hygroscopic and absorb atmospheric water at concentrations as low as 50%.  The formation of NMF from Filaggrin is highly correlated with the water content of the stratum corneum and only occurs within a specific range of water concentrations. When the water content is high, filaggrin is stable, and conversion to NMF does not take place.[3]  Conversely, when the water content is too low, hydrolytic enzymes needed for this reaction are unable to function. The water content of the stratum corneum ranges from 10% to 30% in healthy skin, as compared to 75 to 85% water content of stratum basale.[4] This gradient is a key feature in its function as a barrier.

Organized in a “bricks and mortar” structure, the stratum corneum is composed of a variety of proteins and lipids.[5] Corneocytes have a  tight organization in an interlocking and overlapping fashion, surrounded by a lipid lamella.[3] The major lipids involved in this structure are ceramides, cholesterol, and free fatty acids, which are synthesized by the keratinocytes, and stored in secretory granules.[6][3][1] These granules get released at a slow rate under normal conditions, but upon insult to the barrier, they undergo rapid secretion. The acute barrier disruption results in loss of the calcium gradient, which is an important regulator in the secretion of these granules.[7] 

Issues of Concern

Dry skin has many causes including frequent hand washing, exposure to harsh chemicals, low ambient humidity, as well as medical conditions like atopic dermatitis, ichthyosis, and psoriasis.  The goals of moisturizing the skin are to improve the appearance and function of the skin. In patients with medical conditions associated with impaired barrier function of the skin, like atopic dermatitis, diligent use of moisturizers is a fundamental component of their treatment.[8]

Choice of moisturizing agents can be adjusted to best fit the needs of a patient.  Factors like acne, flaking, hyperkeratosis, itching, or sensitive skin merit consideration when making recommendations of a moisturizing agent.  

Clinical Significance

Types of Moisturizers:

Moisturizers divide into several categories, and their functions include preventing water loss through the skin, adding water to the skin, and reducing visible flakes.  In recent years, with a fuller understanding of the structure and function of the skin barrier, the science of moisturizer development has advanced significantly. Modern moisturizers frequently combine ingredients with different mechanisms of action to achieve specific results.

Occlusive moisturizers prevent evaporation of water or reduce transepidermal water loss (TEWL) from the skin by forming a barrier.  This barrier allows replenishment of the water content of the stratum corneum by the deeper layers of the epidermis and dermis.

Petrolatum is the classic example of an occlusive moisturizer, and it is the most effective.  It reduces water loss through the epidermis by nearly 99%.[9]  Many other substances can serve as occlusive moisturizers:

  • Hydrocarbons: petrolatum, mineral oil, paraffin, squalene
  • Silicones: dimethicone
  • Vegetable oils: coconut oil, castor oil, olive oil, grape seed oil, soybean oil
  • Animal Fats: Mink oil, emu oil, lanolin
  • Wax Esters: Lanolin, beeswax
  • Sterols: Cholesterol, ceramides

Humectants are compounds that attract and bind water.  Some of these substances, like urea, are endogenously present and make up part of the NMF.  Humectants can hydrate the skin if the humidity is more than 70%, but more commonly, will draw water from the deeper epidermis and dermis.  Without concomitant use of an occlusive moisturizer, some humectants can result in an increased transepidermal water loss and exacerbate of skin dryness.  

Alpha-hydroxy acids (AHAs) are an important group of humectant molecules and have more recently been a focus for their use as moisturizing agents, but also in cosmetics. AHAs include glycolic and lactic acids.  These agents impact the water content of the stratum corneum by several mechanisms. They are effective humectants, they promote desquamation by reducing corneocyte cohesion, and also improve the barrier function by increasing levels of ceramides.[3][10] Lactic acid has been used topically at concentrations up to 12% in the treatment of ichthyosis and dry skin for many years.[3]

Urea is a component of NMF. The addition of urea to moisturizers helps with the absorption of water into the stratum corneum, it promotes desquamation of corneocytes and increases penetration of other topically applied medications.[10]  It improves the skin's barrier function and reduces TEWL.[3]  Urea improves itching and is useful in the treatment of ichthyosis, disorders associated with hyperkeratosis, and atopic dermatitis.[8]

Glycerin is another commonly used humectant and is present in many skincare products. In addition to attracting and binding water, it has demonstrated beneficial effects in barrier repair.[10][3] Other humectants include honey, propylene glycol, sorbitol, and hyaluronic acid.

An emulsifier is another classification of ingredients commonly found in moisturizers.  It is a molecule which allows for two immiscible substances to exist as a single phase. The molecules are typically long carbon chains with a polar group.  Commonly used emulsifiers are fatty acids, like stearic acid.[11] 

Formulations

When a moisturizer contains humectants, the water content of the skin more rapidly increases, but as mentioned previously, this does not necessarily reduce trans-epidermal water loss.  Similarly, when using an occlusive agent, the water content of the skin takes a long time to increase, as the water must be drawn from deeper levels of the skin before an improvement takes place.  The term “cream” traditionally refers to a product containing more occlusive ingredients, whereas a “lotion” contains primarily humectants.[11]

Modern moisturizers often contain both occlusives and humectants that contribute to the efficacy.  Understanding the physiology of the skin barrier, and how a disease state or circumstance may contribute to dry skin, impaired barrier function or flaking of the skin can help us choose the best ingredients for a patient. The specific balance and combination of ingredients will help achieve a variety of outcomes depending on the desire of the consumer.

Enhancing Healthcare Team Outcomes

Particularly in the management of chronic medical conditions, like atopic dermatitis, liberal use of moisturizers is a fundamental component of treatment.[8][12]  The application of moisturizers can be time-intensive for patients and caregivers, and as a result, is often neglected. Having consistent discussions by all members of the care teams, including dermatologists, pediatricians, and nurses, is extremely important. 

Dry skin affects millions of people and can seriously affect the quality of life. The use of moisturizers is the simplest way to obtain symptom relief. Hence, nurses, pharmacists, and primary care providers should encourage patients to use moisturizers liberally. However, patients should be educated to select moisturizers that are free of fragrance; the more chemicals in a moisturizer, the more likely is it going to cause an allergic reaction.

The consistent use of moisturizers in atopic dermatitis can reduce symptoms and frequency of disease flares. Numerous randomized controlled trials form the basis of this recommendation. The level and strength of evidence are IA.

Physicians (MDs, DOs, NPs, PAs) need to include moisturizers in their prescribing and care instructions. Pharmacists can make recommendations on the most appropriate types of agents to the prescriber or nursing staff. Nursing will often be in charge of application in the inpatient setting and can assess the effectiveness of moisturizing therapy, or in the outpatient setting can determine compliance with the moisturizing regimen, and report back to the interprofessional healthcare team on the success or failure of treatment. As with any intervention, using moisturizers is most effective with an interprofessional team approach. [Level V]


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Moisturizers - Questions

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What is the function of a hydrous ointment?



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An 18-year-old female presents to the clinic for acne with a topical retinoid and a benzoyl peroxide wash. With treatment, she develops dry flaking skin. What would be the most helpful moisturizing agent to help with her symptoms?



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An 18-month-old patient is brought to the clinic for moderate to severe atopic dermatitis. His parents report a significant impact on the quality of life for their son due to poor sleeping, irritability, and constant itching. They are consistently using topical steroids, with improvement, but experience frequent flares. What is the best way to reduce the frequency of flares?



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A 78-year-old male with a medical history of psoriasis presents to the office with the complaint of dry flaking skin. What is the best recommendation to improve the appearance of his skin?



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A 5-month-old female is brought to the office with her mother for evaluation of an erythematous, edematous rash on her face, neck, arms, and legs. Mother reports that it has been present for 1-2 months and is getting progressively worse. She is sleeping poorly and itching constantly. Family history is positive for seasonal allergies and asthma. What is the best way to address the primary pathogenesis of this disease process?



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Moisturizers - References

References

Madison KC, Barrier function of the skin:     [PubMed]
Verdier-Sévrain S,Bonté F, Skin hydration: a review on its molecular mechanisms. Journal of cosmetic dermatology. 2007 Jun;     [PubMed]
Harding CR,Watkinson A,Rawlings AV,Scott IR, Dry skin, moisturization and corneodesmolysis. International journal of cosmetic science. 2000 Feb;     [PubMed]
Jansen van Rensburg S,Franken A,Du Plessis JL, Measurement of transepidermal water loss, stratum corneum hydration and skin surface pH in occupational settings: A review. Skin research and technology : official journal of International Society for Bioengineering and the Skin (ISBS) [and] International Society for Digital Imaging of Skin (ISDIS) [and] International Society for Skin Imaging (ISSI). 2019 May 20;     [PubMed]
Elias PM, Epidermal lipids, barrier function, and desquamation. The Journal of investigative dermatology. 1983 Jun;     [PubMed]
Lee SH,Elias PM,Proksch E,Menon GK,Mao-Quiang M,Feingold KR, Calcium and potassium are important regulators of barrier homeostasis in murine epidermis. The Journal of clinical investigation. 1992 Feb;     [PubMed]
Meckfessel MH,Brandt S, The structure, function, and importance of ceramides in skin and their use as therapeutic agents in skin-care products. Journal of the American Academy of Dermatology. 2014 Jul;     [PubMed]
van Zuuren EJ,Fedorowicz Z,Arents BWM, Emollients and moisturizers for eczema: abridged Cochrane systematic review including GRADE assessments. The British journal of dermatology. 2017 Nov;     [PubMed]
Iino H,Fujii M,Fujino M,Kohara S,Hashizaki K,Kira H,Koizumi N,Watanabe Y,Utoguchi N, Influence of Characteristics of Oily Vehicle on Skin Penetration of Ufenamate. Biological     [PubMed]
Lodén M, Role of topical emollients and moisturizers in the treatment of dry skin barrier disorders. American journal of clinical dermatology. 2003;     [PubMed]
Lee C,Bajor J,Moaddel T,Subramanian V,Lee JM,Marrero D,Rocha S,Tharp MD, Principles of Moisturizer Product Design Journal of drugs in dermatology : JDD. 2019 Jan 1;     [PubMed]
van Zuuren EJ,Fedorowicz Z,Christensen R,Lavrijsen A,Arents BWM, Emollients and moisturisers for eczema. The Cochrane database of systematic reviews. 2017 Feb 6;     [PubMed]

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