Benefits of Disposable Baby Wipes for Cleaning Diapered Skin of Pre-Term and Term Infants

Benefits of Disposable Baby Wipes for Cleaning Diapered Skin of Pre-term and Term Infants

Josh Gregorio, PhD, Corey Cunningham, PhD, and David Koenig, PhD, Kimberly-Clark Corp., 2015

The skin is a stretchable, rugged, sensitive, self-healing organ and perhaps our most versatile body part. Skin maintains body temperature, retains essential fluids, and protects the body from toxic agents, microorganisms, and harmful ultraviolet rays.1 The skin is often taken for granted because it is so effective in performing its duties. Skin care begins with the appropriate cleaning regimen.

Premature infant skin physiology and cleansing considerations

Premature infant skin is very delicate and lacks effective barrier protection as the stratum corneum, the outermost layer of the skin, has not fully developed. Consequently, premature infants have extremely high transepidermal water loss (TEWL) through their skin and are more vulnerable to exogenous insults and stresses.2-3 Coupled with weak resilience and structural integrity, the diapered environment can create even greater challenges for maintaining skin health. For example, it has been extensively shown that skin occlusion leads to over-hydration, resulting in compromised skin strength and reduced barrier function.4 Moreover, skin irritants present in feces and urine can induce skin rash through a variety of mechanisms including increased skin pH, proteolytic breakdown of stratum corneum proteins and cell membrane integrity, and permeation of bile salts and other contact irritants into the epidermis.5-6

It is also known that pre-term infants are at an increased risk of developing diaper dermatitis as their skin barrier (stratum corneum) is not fully formed yet.7 In fact, infants born at gestational age less than 25 weeks only have one half the thickness of both the stratum corneum and the underlying epidermis relative to full term neonates.8-10 Thus, premature infant skin is very permeable to both water and irritants. Additionally, infants born at less than 28 gestational weeks lack an outer protective layer called the vernix caseosa. Taken together, premature infants suffer from increased water evaporation from their skin.5 It is estimated to take 2-9 weeks after birth for the skin to fully form in these pre-term babies.5 Table 1 highlights differences in skin development between full-term and pre-term infants and the consequences of these differences, whereas Figure 1 illustrates key differences in skin morphology.

Public Table 1: Physiological Differences in Full-term and Pre-term Skin Skin Characteristic Full-term Pre-term Consequence Epidermal thickness 40-50 um 20-25 um Delayed skin maturation Stratum corneum ↑ water loss Normal Poor development ↑ Permeability of topical agents Cell attachment Normal Fewer ↑blistering ↓collagen ↓elasticity Dermis Normal ↓elastic fibers ↓strength Fat Normal Lower ↑hypothermia Melanocytes Normal ⅓ of full-term ↑photosensitivity Acid mantle ↓antimicrobial defense ↑moisture Normal Delayed development loss, ↑ irritation Adapted from Ness.11

Figure 1: Stratum corneum and epidermis are incomplete in 25 week gestational age pre- term (left) compared to full-term neonates (right).

Why Cleaning is Important

Regularly cleaning diapered skin without causing mechanical abrasion or chemical-induced stress is essential to maintain skin health. The concern for the latter has led many skilled

Public health care practitioners and mothers alike to adopt a skin cleaning regimen consisting of a cotton cloth/ball and water. It is the view of many that disposable baby wipes might cause more harm than water and cotton alone, especially in infants with sensitive skin or in infants experiencing diaper rash.12,13 This concern, although well intended, is misplaced. Many clinical studies have evaluated the use of disposable baby wipes and compared them to water and cloth with and without soap. The preponderance of the data developed in such studies demonstrate the benefits of pre-moistened disposable baby wipes. Using various methods to analyze skin health, clinical researchers have demonstrated that disposable baby wipe use leads to lower erythema, less damage to skin barrier function as measured by transepidermal water loss (TEWL), better maintenance of skin pH, and less irritation when compared to the use of water and cotton or water, cotton and soap.14-16

Clinical studies have shown benefits of the use of disposable baby wipes in pre-term and term infants from birth up to 24 months and in seriously ill neonates, as well as infants with clinically diagnosed atopic dermatitis. For instance, a study involving 53 infants, conducted over a 4 week period, evaluated the use of disposable baby wipes on infants with clinically diagnosed atopic dermatitis (sensitive skin). The mean number of wipes applied to the infants was 12 per day. Their results showed that the incidence of erythema dropped from 34% at day 1 to 14% at day 29 of the study and the investigators concluded that pre- moistened baby wipes were suitable for everyday cleaning of sensitive diapered skin.14 Similarly, in a double blinded study involving 102 infants over a 2 week period, disposable baby wipes were compared to water plus a cleaning material (mostly cotton wool balls) in 6 to 24 month old infants. The study found that diaper rash was significantly lower in the skinfolds area of infants who were cleaned with disposable baby wipes compared to those cleaned with water and cleansing materials.14 Another skin care study was conducted to evaluate wipe use in a level III NICU and demonstrated the benefits of disposable baby wipes vs. cloth and water towards maintaining balanced skin pH.3 This study compared disposable baby wipes at pH ranges lower than those found in water and compared them to water and cloth. Strikingly, the study showed that significantly less skin barrier disruption (lower TEWL) was observed and that perineal erythema were significantly lower in the wipe groups compared to the water and cloth groups. The authors noted that the lower pH in the disposable baby wipes led to a lower skin pH relative to infants in the water and cloth group, suggesting that baby wipes aided in preserving the skin’s acid mantle.3 The importance of maintaining a low skin pH has been evaluated in many studies, highlighting the significance for establishing the acid mantle in skin, a key defensive attribute. At birth, the pH of skin is around 6.5 – 7, but continues to drop to around 5.5 after several days, weeks, or months.17 The acid mantle is important in promoting skin health and function by permitting stratum corneum maturation and preventing colonization of pathogenic microorganisms. Premature infants are even more prone to skin colonization by pathogens

Public as it takes much longer for the establishment of the skin’s acid mantle and stratum corneum development to occur (up to 8 weeks after birth). Therefore, any diapered skin cleansing strategy needs to take this into consideration.

The source of water used can factor greatly in the potential to harm skin, when incorporated into a skin cleansing method. Tap water can have a pH up to 8.5, distilled water can range from pH 6.5-7.0, and neither water source provides buffering capacity.18,19 The cleansing solutions used in the manufacture of contemporary disposable baby wipes, although over 90% water, are typically formulated to have a final pH in the range of 4.5-6.5 and are designed to have good buffering capacity to maintain the target pH (Figure 2). Maintaining skin pH around 5.5 helps stratum corneum development, improves barrier function (reducing water loss), and helps protect against microbial colonization.17,20-23

Figure 2: Disposable baby wipes are formulated to complement healthy skin pH. The pH of water can be as high as 8.5.

A recent report attributes rash development to an imbalance of skin pH following exposure to urine and feces.24 This mixture leads to activation of digestive enzymes present in feces that can damage the stratum corneum through degradation of lipids and proteins in the skin.2,24 Infant feces contains lipolytic and hydrophobic enzymes that are immiscible in water. Cleansing practices that only include water may not adequately remove these materials and can result in stratum corneum damage and rash development. Effective removal of lipid soluble lipolytic enzymes requires surfactants or detergents to emulsify and trap them into surfactant micelles (droplets).25 It has been shown that mild surfactants can be effectively used to remove these harmful substances without compromising skin health. Thus, many contemporary disposable baby wipes contain low concentrations of mild surfactants to accomplish this task while affording skin benefits that water and cloth alone cannot provide.

Public Considerations for Cleansing Diapered Skin

Cleaning the skin is the major benefit of personal care wipe products like disposable baby wipes. In the case of perineal skin, microorganisms and other fecal-derived soils present unique challenges. Furthermore, infant stool contains a variety of secretions that can be found on diapered skin (Table 2).

The major soil on infant skin during diaper use is feces. The normal daily stool of human is about 250 g. Normal feces are roughly 75% water and 25% solids.26 The bulk of fecal solids are bacteria and undigested organic matter and fiber. More than 75 different kinds of bacteria are found in feces.27 Other constituents are digestive secretions, enzymes, fats, cell debris, electrolytes, water, and small amounts of protein.26 The characteristic brown color of feces is due to stercobilin and urobinin, both of which are produced by bacterial degradation of bilirubin. Fecal odor results from gases produced by bacterial metabolism, including skatole, mercaptans, and hydrogen sulfide.26 Microorganisms, which constitute a large portion of fecal dry weight, attach to the skin by multiple mechanisms, requiring a complex removal strategy employing surfactant action, shear forces, and affinity binding. The understanding of these interactions, and the role they play in the tightness of binding of the soil to skin, is imperative in the development of safe, gentle, yet effective cleaning technologies for inclusion into disposable baby wipes.

Table 2: Soils and Soil Components Relevant to Diapered Skin Secretion Description Source Mucus Composed of secretions from the mucopolysaccharide rich Oral, Nasal, Uro- glands, inorganic salts, desquamated cells, and leucocytes Genital, GI Bile Derived from cholesterol in liver, modified by bacteria in GI intestine. Important for digestion and absorption of fat Gastric juices Secreted by stomach mucosa. Consists of HCl, pepsinogen, GI intrinsic factor, gastrin, mucus, and bicarbonate buffers Pancreatic juice Consists of insulin, glucagon, pancreatic enzymes (trypsin GI and chymotrypsin) for digestion of fats and proteins in small intestine. Feces Consists of bacteria, cells exfoliated from the intestines, GI non-degraded digestive enzymes, and a small amount of food residue. Urine Aqueous solution of urea, salt, and uric acid, with some GI hippuric acid and pigments. Usually ~96% water to ~4% solid matter Smegma Sebaceous matter that collects between the glans penis and GI the foreskin

Public Not surprisingly, an infant’s diet can have an impact on fecal composition. While infant stool solids are primarily composed of bacteria and mucin, calcium and fatty acid soaps are also present. Stools from formula-fed infants have higher solids content and contain higher levels of minerals and lipids and considerably less carbohydrates than breast feed infants. Differences in fecal lipids derived from formula- and breast-fed infant stools are due almost entirely to fatty acids (mainly C16:0 and C18:0) excreted as soaps.28 Fatty acid soaps, predominantly saturated, accounted for one third of the stool dry weight of breast fed infant stools. Additionally, there is a significant difference in the microbiota of stools collected from breast fed and formula fed infants (Table 3).29,30

Table 3: Predominant Microbes in Infant Feces Breast Fed Milk Fed / Solid Food Bifidobacteria (90%) Bifidobacteria Enterobacteriaceae Lactobacilli Enterococci (~9%) Bacteroides, Staphlococci, Lactobacilli, Clostridia, Bacteroides, Enterococci Clostridia (~1%)

To remove all these soils from the skin an efficient cleaning process is required. Cleaning of skin can be divided into three processes. The first is a traditional wash, or bath, wherein the soil is removed primarily with a solution containing a surfactant. The second is a dry wipe, such as a bath tissue our hand towel, in which soil is removed through the physical process of wiping the skin. The third process is the combination of a solution and wipe in what is commonly marketed as a wet wipe. Disposable baby wipes provide convenient cleaning advantages by combining the action of both a surfactant solution and the wiping action of a towel or tissue.

Most solution-based skin cleansing products remove soils primarily through surfactant or detergency action. This cleaning action uses physicochemical processes leading to the removal of soil from the surface of the skin. Cleansing action results from the presence of surface-active agents (surfactants), which are capable of forming an adsorption solvation layer around the dispersed-phase particles (soil) and on the cleansed surface.31 The high surface activity of such compounds is required for efficient dispersion and removal of soil from the skin.

The initial stage of solution based cleansing is the wetting of the soiled surface by lowering surface tension. The emulsification of liquid soils is usually accompanied by their dissolution into micelles of the cleansing agent. The introduction of various inactive

Public additives (salts and water-soluble polymers) increases the cleansing action of soaps and especially of synthetic detergents. The combined use of various types of surface-active agents in detergents usually increases the efficiency of the cleansing agents. As some surfactants can be irritating to the skin, extreme care must be taken when developing a cleansing solution.32

In contrast, a dry application, such as bath tissue, cleans soil from the skin as a result of shear force, affinity, or a combination of the two. Friction is defined as the force that resists relative motion between two bodies in contact.33 This motion produces stresses and strains on both the bath tissue and soil on the skin, thereby releasing the soil from the skin once the energy thresholds are overcome. Stress is the force exerted when one body presses on, pulls on, pushes against, or tends to compress or twist another body, as can be seen in the motion of bath tissue across skin.34 Strain is the deformation of a material body (cleansing wipe) under the action of an applied force.33 Friction is thought to cause the most damage to the skin during the cleaning process.35 Dry wiping of the skin can leave a significant amount of fecal material behind on the skin as well as cause skin damage. The inclusion of water can greatly increase the cleaning performance and reduce skin damage.

The mechanism of action for a baby wipe is a hybrid of solution-based and dry wipe cleaning processes. For the soil to be removed from the skin the adhesion forces between the soil and skin must be overcome. These adhesion forces are a combination of van der Waals, electrostatic, and capillary forces.

When a baby wipe is used, a number of release forces are available for the cleaning process that are not available to a solution or dry wipe alone. These forces include drag, net buoyancy, and capillary forces (Figure 3). As a wet wipe is moved across the skin, a liquid front is pushed in front of the wipe, creating a shear drag force that is parallel to the wiping motion that helps release the soil. The net buoyancy force depends on the relative densities of the liquid and the soil. In most cases, the relative density of the particle is reduced due to the presence of water. Wet wipes also provide a capillary force that aid in removal of feces from the skin. Specifically, disposable baby wipes may alter existing capillary forces between skin and feces or may reduce surface tension between feces and skin to decrease adhesion. The addition of surfactants to the wet wipe solution provides a way to counteract both adhesion forces and associated capillary forces that bind many soils to the skin.36

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Figure 3: Wiping interactions on skin

Disposable baby wipes are a common method used for cleaning diapered skin. A baby wipe provides a wetting solution that reduces both the electrostatic forces of adhesion of the soil to skin as well as decreasing the capillary forces. Additionally, the force of the material against the skin provides a shear stress to aid in removal. The baby wipe then can trap the soil removing it once it is released from the skin. Once trapped on the wipe, the soil is less likely to be re-deposited. Wiping the skin with a fresh wipe surface also acts like a rinsing step to ensure no residual soil remains on the skin. Critical to the whole process is the level of wetness of the wipe. The optimum range is defined by the wipe substrate type, solution wetting the wipe, and the application. A baby wipe that is too dry or too wet will not trap soil well. The dry baby wipe just pushes the soil around on the skin while the overly moist baby wipe will entrain the soil contaminants in the solution allowing for re-deposition onto the skin. Most commercial baby wipes have tightly controlled wetness levels to maximize the cleaning and trapping process.

The Evolution of Wiping Substrates

Baby wipes were first introduced in the 1990’s and the major share of the disposable baby wipe market was occupied by Kimberly-Clark’s HUGGIES® and Procter & Gamble’s Pampers® brands. This is still true today, despite the gains in the market by smaller, private label manufacturers. Regardless of the company selling it, the wipe consists of three main components – substrate, formulation, and package. All of these components have changed

Public dramatically over the years resulting in a more functional and aesthetically pleasing product.

The first baby wipe products consisted of substrates made from carded rayon fibers held together with adhesive binders. These wipes were strong and thin, but had a rough surface. In the mid-1990’s, the introduction of air-laid nonwovens dramatically changed the wipe. Constructed of wood pulp, polyester and adhesive binders, these air-laid wipes were much softer and thicker. Coform, which combines meltblown polypropylene fibers and pulp to produce a highly absorbent material with outstanding wet integrity was developed in the late 1990’s by Kimberly-Clark as a competitive technology to the initial adhesive bonded air-laid.

The mid 1990’s saw further modification to air-laid nonwovens as companies altered fiber composition and fiber to polymer blend to optimize performance. Bi-component fibers, which were also developed in the 1990’s and combining two polymers into each fiber, once again improved the attributes of air-laid producing substrates with increased strength, softness, and thickness. Despite these innovations, coform is considered to be a premium product and continues to evolve.

In the 1990’s, two new substrate forming technologies, thermal bonding and hydro- entanglement, were developed and have been utilized. The first, thermal bonded, used heat to hold the wood pulp and polypropylene together. One common variant made by this process is spunbond. Spunbond is a strong, flexible material manufactured with continuous fibers that are thermally bonded to create a fabric. Hydroentangled, also known as spunlaced or water weaving, entwines individual fibers with high pressure jets of water. Both of these new processes were advantageous as they eliminated the use of adhesives and allowed for wider fiber choices. Today, premium wipe products may utilize any one of these processes to offer the delivery of very soft, low abrasion, cloth-like wipes to the baby care market.

Disposable Baby Wipes that Address Pre-term Infant Skin Cleansing Needs: Wipe Formulation Considerations

Formulating cleansing wipes for infants is difficult as there are many factors to consider in the development process.38 The ideal baby wipe contains: 1) a large percentage of water; 2) an extremely mild surfactant system that lowers surface tension to wet-out soils while not irritating skin or removing skin lipids; 3) ingredients that enhance glide across the skin to minimize frictional damage during the wiping process,39 4) finally, a preservation system

Public that ensures product freshness while not irritating the skin. Optional emollient ingredients could be present that help replenish lipid components in the skin through deposition.

For the general population, surfactant systems typically utilized in name brand and private label wipes are well tolerated. The amount of surfactant is typically less than 1% and most companies use amphoteric surfactants such as Coco-Betaine, Cocamidopropyl Betaine and Sodium Cocoamphoacetate. Amphoteric surfactants contain both a positive and negative charge on the molecule. These surfactants are an ideal choice for baby wipes as they are much less irritating than typical anionic and cationic surfactants found in many shampoos, hand & body washes and antibacterial hand soaps.

For individuals with under-developed or damaged skin barrier, such as premature infants, the use of wipes with non-ionic surfactants reduce the irritation potential relative to other surfactants. Such non-ionic surfactants would include Polysorbate 20, Glyceryl Stearate and Bis-PEG/PPG-16/16 PEG/PPG-16/16 Dimethicone.

To enhance the glide of the wipe across the skin (i.e. reduce the friction), well known body lotion ingredients like Dimethicone are advantageous. Other, less common skin emollients such as Ethylhexyl Stearate and Cetearyl Isonononate can enhance glide as well. These long chain fatty esters form a thin layer between the wipe and skin and reduce friction.

Probably the most important aspect of a baby wipe is the preservative system. While the popular media often seems to suggest that all preservatives are ‘bad’ and do more harm than good, the exact opposite is true. If preservatives were not present in the formulation, there would be a high risk of microbial contamination of the product before or after first use. Beyond aesthetic considerations for the product such as off-color, odor, and poor tactile aesthetics, such contamination could lead to serious infections.

While there are preservatives that can cause sensitization (i.e. Methylisothiazolinone), these have been removed from all branded wipes within the last two years and can only be found in a few private label and hospital brand wipes. Other preservatives with questionable safety profiles, such as formaldehyde donors (i.e. DMDM Hydantoin, Sodium Hydroxymethylglycinate) have been absent from almost all wipe products for the last five years. Virtually every preservative system has some potential to illicit an irritation response in some sub-population. The goal of every product is to reduce this probability. Preservative and preservative-enhancing ingredients that are very well tolerated include Sodium Benzoate/Benzoic Acid, Potassium Sorbate/Sorbic Acid, Caprylyl Glycol and Disodium EDTA.

Public In addition to the required aspects of every baby wipe, there exists the opportunity to include specialty ingredients for specific wipe applications that provide specific skin health benefits. For example, emollients can be included to enhance skin barrier function. Humectants (water-loving moisturizers) like Glycerin can help to improve the water retention of the skin to afford moisturization benefits. Oil soluble emollients like Behenyl Alcohol, Stearyl Alcohol, Stearic Acid and triglycerides help the skin barrier by depositing lipid-like substances that may get stripped away during bathing. Importantly, Behenyl and Stearyl alcohols, unlike Ethanol and Isopropanol, do not irritate the skin or elicit “stinging” sensations.

In conclusion, despite the under-developed and compromised skin conditions experienced by pre-term infants, baby wipes effectively remove harmful soils (see Table 2) while maintaining skin health. Numerous clinical studies in pre-term infants have demonstrated that formulated baby wipes are both well tolerated and promote acid mantle development of the skin. The deleterious consequences of prolonged fecal and urine insults on skin health have been well documented. Formulated baby wipes, as opposed to the use of water and cloth, or water and cotton wool, can provide additional benefits to effectively remove soils from diapered skin. Importantly, feces contains both hydrophobic (water fearing) and hydrophilic (water loving) compounds. Effective cleansing regimens must be able to effectively remove both. Formulated baby wipes, designed with this premise in mind, effectively remove hydrophobic and hydrophilic materials whereas the use of water and cloth, or water and cotton wool, cannot afford the benefits conferred by baby wipes (Figure 4). Thus, cleansing regimens based on water and cotton cloth/wool can leave potentially harmful irritants on the skin that can lead to skin breakdown and rash.

Figure 4: Disposable baby wipes contain surfactants that can effectively remove both hydrophobic and hydrophilic fecal material unlike water and cloth. In addition, studies conducted in pre-term and term infants have demonstrated that the use of disposable baby wipes leads to reduced skin redness and irritation, decrease water loss, and balanced skin pH relative to the use of water and cotton/cloth.

Public References

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