New Developments In Understanding Of Sensitive Skin

Sensitive skin is a condition of subjective cutaneous hyperreactivity to environmental factors. Subjects experiencing this condition report exaggerated reactions when their skin is in contact with cosmetics, soaps, and sunscreens and they often report worsening after exposure to dry and cold climates.

Recent findings support the connection between skin microbiota and sensitive skin. Neurohormones diffuse in sweat and epidermis leading skin bacterial microflora to be largely exposed to these host factors. Bacteria can sense a multitude of neurohormones. Substance P (SP) is stimulating the virulence of Bacillus and Staphylococci. The action of SP is highly specific with a threshold below the nanometer level. In a recent study of the mycobiome of sensitive skin was more phylogenetically diverse than that of non-sensitive skin. Lactobacillus and Mucor racemosus were more abundant on sensitive skin than nonsensitive skin, whereas Malassezia restricta was less abundant. Both skin microbiome and mycobiome varied according to the perceived skin sensitivities of the subjects.

Sensitive skin is not limited to the face and the scalp is an area frequently involved: sensitive scalp showed disrupted barrier function, abnormal sebum amount and composition, as well as the perturbed microbiome, which might be the direct cause. The role of microbiome and mycobiome in sensitive skin needs more investigation as well as the possible neurogenic alterations. A complete understanding of this peculiar syndrome may lead to the development of new and more effective pharmacologic and cosmetic treatments.

Bibliography

Misery, Laurent. 2023. “Sensitive Skin Testing.” In Handbook of Cosmetics Science and Technology, by Elsa Jungman, Kazutami Sakamoto, Howard I. Maibach Frank Dreher, 182-189. Boca Raton, London, New York: CRC Press.

Baby Care Products For Skin And Hair

The primary care products that come in contact with baby skin are diapers and cosmetics. Baby cosmetics can be mainly subdivided in two groups, namely cleansing and protecting cosmetics. Recently there is an increase in baby care products that contain natural ingredients or fewer ingredients, however non-all-natural products like certain plant extracts, are recommended to be used on skin. Certain ingredients like perfumes, could lead to skin reactions and should be avoided in baby products, unless considered safe for use on baby. Other ingredients, like preservatives make sense in products where microorganisms can be a risk, like in aqueous based products.

When formulating products there are several factors that need to be considered and it is recommended to work together with experts like toxicologists and microbiologists to ensure the product is safe to use on baby skin. Some ingredients may also be prohibited or restricted in certain countries and experts need to be consulted to ensure that the product is allowed to be marketed and sold in that country.

Hygiene Products: Diapers

The most appropriate strategy for diaper rash is prophylaxis, including keeping the skin clean and dry. Introduction of superabsorbent polymers is used to turn urine into gel. These are absorbent particles that can absorb huge amounts of liquid and therefore help keep the diapers thin but highly absorbent.

Cleansing Cosmetics

Surfactants and Soaps:

Bathing a baby for 5-7 minutes in lukewarm water (35-36°C) usually is sufficient. Better is to use so-called secondary tensides, including nonionics and amphoterics, or mild anionics such as sulfosuccinates, isethionates, and protein fatty acids condensates.

The use of bath foam is not suitable for babies because of its high content of primary tensides producing excessive foam. Parents often think that foam is important for its cleansing properties but foam has no cleansing function, and the ingredients required to produce a sufficient amount of stable foam are often quite irritating and not suitable to be used in baby shampoo, e.g., alkyl sulfates, and alkyl ether sulfates.

Emulsions and Oils:

For cleansing of the baby and in particular the diaper zone, liquid cleansers based on oil-in-water (o/w) emulsions are often used, especially when water and washcloth are not well tolerated by the baby’s skin.

When a baby is prone to contact dermatitis, it is advised to screen the ingredients list because those tissues often contain high concentrations of preservatives, necessary to prevent microbiological contamination of the tissues.

Baby Wipes

Over the last two decades disposable baby wipes have been developed as an alternative to traditional cleansing methods. Wipes consist of a nonwoven carrier material soaked with an emulsion-type, watery or oily lotion. Cleansing studies confirmed that high-quality baby wipes are suitable for daily cleansing of the diaper area, of healthy babies as well as of babies with comprised, irritated skin, on newborn infants and on atopic and premature populations. A cleansing baby wipes with sufficient pH buffering capacity offers an opportunity to stabilize skin pH at physiologic levels and thus help to overcome the potentially detrimental effects of an elevated skin pH in the diaper area.

Protecting Cosmetics

Emollients/Lotions

In good skin care of diaper zone, the application of emollients plays an important role, and the application of a cream layer can create an effective protective barrier. Protective emollients like petrolatum for the nappy zone are preventive or protect the skin against aggressions from urine, feces, and their interactions. Zinc Oxide (ZnO) is an often-used component in diaper rash protection products but may be considered a cosmetic or drug depending on the country. Allantoin, alpha-bisabolol, Aloe vera extract and silicones can be added to improve water resistance.

Powder

Talc powders are not often applied anymore in the diaper area. They absorb moisture, decrease maceration and help prevent irritation of the baby skin. Talc is susceptible to contamination with microorganisms and needs sterilization.

Bibliography

Susanna Brink, M. O. (2023). Baby Care Products. In E. J. Frank Dreher, Handbook of Cosmetic Science and Technology (pp. 339-340). Boca Raton, FL: CRC Press.

Safety Considerations For Baby Care Products

To bring safe baby cosmetics on the market, risk assessment is a key priority and often includes a broadly recognized iterative four-step quantitative exposure-based risk assessment process (US National Academy of Sciences, WHO and the European Union’s Society Scientific Committee on Consumer Safety and Bureau of Indian Standards IS 4011:2018.

The potential impact of skin irritation on dermal absorption should be taken into consideration during baby cosmetic product development.

A distinction should be made between intact, healthy skin and the potentially damaged skin of the nappy zone for which risk factors exist, which are not present for the rest of the body.

The increased prevalence of allergic contact dermatitis in children has prompted scrutiny of products marketed for neonates and children for the presence of sanitisers.

Criteria

During the development of baby products, a number of criteria should be taken into consideration:

• High quality of raw materials in terms of purity, stability, and microbiology via appropriate Certificate of Analysis (CoA).
• Skin Irritation, which is dose-dependent, can be controlled by avoiding well-known irritative ingredients and/or reducing the concentration or frequency of application.
• The presence of sanitizing molecules such as perfume ingredients, even when IFRA (International Fragrance Association) – tested and/or excluding the 26 allergens taken up in regulations, should be avoided if they are not found to be safe.
• The product information file of baby cosmetics, safety data of all ingredients and the finished product, together with a dedicated risk assessment, carried out by a safety assessor, should be present. It should be indicated what specific measures have been taken for baby skin.
• Special attention should be given to the concentration of (i) reactive substances (ii) promotional additives, ‘natural’ and ‘exotic’ ingredients, complex mixtures, plant extracts and animal-derived ingredients or any ingredient from a questionable, impure source; (iii) potential allergens, penetration enhancers, aggressive organic solvents, highly detersive or foaming agents, and antiseptics in particular in daily use products; and (iv) concentrations of preservatives.
• Good practice is: (i) to protect unsaturated lipids from oxidative reactions by adding anti-oxidants; (ii) to adjust and buffer the pH of the final product to skin-friendly pH between 4.5 and 6; (iii) to add chelating or sequestering agents to prevent heavy metal precipitation and protect the preservative system; and (iv) to use known protective skin barrier ingredients.

Dermal Absorption

Dermal absorption data is compound-dependent, varying molecular weight, hydrophobicity
| hydrophilicity, structure, etc., and frequently determined using adult skin.

• The surface area | body weight ratio is 2.3-fold higher in newborns than in adults decreasing to 1.8-fold at 6 and 12 months, respectively. Application of the same amount of product on a similar body surface of baby versus adult could result in higher blood and tissue concentrations in the newborn.
• Pharmacokinetic parameters differ widely between babies and adults and result in reduced clearance and/or a longer half-life of bioavailable substances, thus increasing the potential risk for adverse reactions in babies. Concerning the total body water content, it is known that infants have a higher water content (80-90%) compared to those of adults, which steadily decreases to 55-60%

Another pharmacokinetic difference is a decreased protein binding capacity which can be linked to lower concentrations of glycoproteins in the plasma of infants.

Full-term neonates, tend to show a three to nine times longer pharmacokinetic half-life than adults.

• The SC thickness is reported to be the rate limiting part for percutaneous penetration and thus dermal absorption. The SC is thinner in baby versus adult skin, as measured by confocal laser scanning microscopy, and needs to be considered. The path that molecules have to follow to penetrate the SC layer is potentially shorter.

Importantly, the SC’s barrier is functional at birth and matures for many key skin characteristics (skin pH) in the first few months after birth.

• In use conditions of topical products also play a role. Cosmetic skin care products often are applied onto large body surfaces, e.g., cleansing lotions, sunscreens, etc., increasing not only the potential risk for local effects but also dermal absorption and potential systemic toxicity. This factor is considered in exposure-based risk assessments.
• The Diaper Area and non-diapered regions are indistinguishable at birth but show differential behavior over the first 14 days, with the diapered region having a higher pH and increased hydration. Innovative hygiene absorbent and baby care products, however, provide an increasingly good skin compatibility profile, making the frequency and severity of DD decline.
• Other important factors for dermal absorption are SC hydration and skin pH. For instance, differences in skin pH change the ionization grade of molecules and will influence dermal absorption.

Bibliography

Susanna Brink, M. O. (2023). Baby Care Products. In E. J. Frank Dreher, Handbook of Cosmetic Science and Technology (pp. 339-340). Boca Raton, FL: CRC Press.