Neonatal Skin Care and Toxicology

Gene–environment interaction

A number of genetic and environmental factors are known to interact producing negative consequences for the structure and function of the skin barrier, especially during the period of postnatal skin development. FLG gene mutations resulting in loss of functional filaggrin and its downstream products are the most significant genetic risk factors for the development of AD identified so far, and account for between 15% and 50% of cases, dependent on severity. Carriers of FLG loss-of-function mutations with AD exhibit a more pronounced skin barrier defect, characterized by elevated TEWL, increased skin surface pH and decreased SCH, compared with AD patients without these mutations. Having an FLG loss-of-function mutation likely affects the development of the skin barrier from birth, but alone may not lead to AD; additional genetic and environmental factors are implicated ( Fig. 5.3 ).

Washing the skin with soap and harsh detergents is known to exacerbate AD and other dry skin conditions, especially where the wash water is hard. A single wash with soap or the anionic surfactant sodium lauryl sulphate (SLS) elevates TEWL and skin surface pH and decreases SCH. Washing with hard water leads to increased soap use and soap deposition on the skin, leading to increased dryness (decreased SCH) and irritation. Furthermore, hard water contains high levels of free calcium, which has been shown in vitro to inhibit skin barrier repair. Combining soap or harsh detergents with hard water is thought to result in exaggerated skin barrier damage and prolonged recovery, which may facilitate the development of conditions involving a skin barrier defect. Indeed, living in a hard water area is significantly associated with increased risk of developing AD. A clinical trial in 2008 reported no effect on the severity of AD associated with the installation of a water softener. The study did not address, however, the role of wash product interaction with the wash water, the effect of the intervention on development of AD or the nature of the intervention itself (the water softening systems used do not remove all calcium ions, unlike ultrapure water softeners, and do not alter the alkalinity of the wash water). Further research is required to elucidate the role of water hardness. Current guidelines for the treatment of AD recommend the avoidance of soap and harsh detergents, such as SLS along with other negative environmental factors.

In infants, saliva, nasal secretions and some foods are important environmental factors that interact with genetic variants to exacerbate the skin barrier defect. Saliva contains proteases and lipases and has a pH of 7.42 (±0.4) with a substantial buffering capacity. This provides an optimal pH for protease activity and therefore facilitates skin barrier breakdown. Similarly, breast milk has a pH of 7.29 (±0.19), and nasal secretions have a pH of 6.91 (±0.06), optimal for protease activity. The combination of saliva, breast milk and nasal secretions caught under a pacifier in a baby with AD leads to a localized ‘drooling dermatitis’ around the mouth and onto the cheeks. A combination of adverse environmental factors also contributes to diaper (napkin) dermatitis; urine and feces in conjunction with diaper occlusion, yields elevated skin surface pH and are the sources of additional degradatory proteases and lipases. The interaction of these negative factors at the diaper area has been shown to affect development of the skin barrier at this site.

Drooling dermatitis may play a role in the development of food allergy. The route of sensitization to some food allergens, such as peanuts, is thought to be through the skin rather than by ingestion. This supports the observation that the development of AD is often linked to the development of other atopic conditions, including food allergy and asthma. The increased risk of further progression along the atopic march highlights the importance of more effective treatment of dermatitis in infants. In the case of drooling dermatitis, avoiding pacifiers and the use of barrier emollients to reduce epidermal damage by saliva (and some foods) should be combined with effective cleansing of the face using products that do not damage the skin barrier.

The continued development (optimization) of the skin barrier and the interplay of negative environmental factors affecting infant skin, raise the importance of how our skin is cared for during the first 2 years of life. While we cannot change the genetics of a neonate or infant, we can modify environmental exposures to help prevent further damage to the skin barrier.

Skin cleansing

For both children and adults, bathing is a hygienic necessity. The goal of hygiene is the preservation of skin health. However, there is a balance between cleansing the skin and preservation of its homeostatic properties such as skin barrier integrity. Cleansing is essential to remove pathogenic bacteria such as those from feces. Feces, saliva and other body secretions contain enzymes such as lipases and proteases that breakdown the skin barrier. However, frequent bathing of infants is more of a cultural and aesthetic practice that allows for tactile interaction with the caregiver. Benefits must be carefully considered along with the detrimental effects that can occur with bathing, especially in premature infants.

A balance needs to be reached between the frequency of bathing to achieve optimal cleansing and maintaining an intact skin barrier. For neonates, bathing can lead to hypothermia, increased oxygen consumption, respiratory distress, and destabilized vital signs. Therefore, the first bath should be delayed until after vital signs and temperature have remained stable for at least 2–4 h. Immersion bathing, when feasible, may be beneficial from a developmental perspective. It is more soothing, and can promote enhanced sleep, and in studies, was not associated with significant differences in oxygen saturation, respiratory rate, or heart rate in premature infants of less than 32 weeks' gestation. The water level should be high enough to cover the infant's entire body to aid temperature control and decrease evaporative heat loss. The optimal temperature of bath water is 100.4°F, which should always be accurately measured. Second-degree burns have been reported after immersion into overly hot bath water tested only by touch. Sponge bathing with a moistened cotton ball or cloth is an acceptable alternative. Immediately after bathing, the infant's skin should be gently towel dried and a head covering applied.

Vernix caseosa, composed of sebaceous gland secretions, desquamated skin cells, and shed lanugo hairs, is negligible in preterm infants. Vernix need not be removed, as this layer may aid in thermoregulation, hydration, bacterial protection, and wound healing.

The first bath should be given respecting universal precautions to limit contact with transmissible pathogens. The optimal frequency of bathing is open to debate. Research suggests that bathing twice a week will not affect TEWL or skin surface pH, assuming that mild products are used, and as such, Blume-Peytavi and colleagues recommend that bathing take place no more frequently than every other day.

The use of water alone or water with added skin cleaning products for bathing has led to considerable debate. Soaps and cleansers containing harsh detergents, such as SLS increase skin surface pH and reduce SCH. Conversely, washing with tap water alone leads to the extraction of water-soluble metabolites from the skin, including NMF, and causes mild irritation and increased skin dryness. Furthermore, water alone is ineffective at removing fat-soluble substances from the skin. The surfactants in cleansers are required to remove these potential fat-soluble irritants. A balance is therefore required between effective cleansing and the need for the mildest surfactants. SLS is a very effective cleanser, however it is very irritating to the skin, partly associated with its alkaline property. Wash products designed for use on babies' skin contain very mild surfactant complexes and are buffered to skin pH in order to minimize the negative effects on the skin barrier associated with alkaline wash products.

The use of cleansing products compared with water alone for bathing newborns has been subject to a systematic review, which focused on two trials. One study comprised of four trial arms, including washing twice weekly with a wash gel product; bathing twice weekly with water, then applying a cream; bathing with wash gel and applying cream after bathing; and bathing with water only. The second study compared two different liquid cleansers with water for bathing infants. The results of these studies indicated no harm to skin barrier function with the tested cleaning agents, although the number of babies in each treatment arm was small. A large UK-based trial of a mild pH 5.5 liquid SLS-free cleanser versus water alone in bathing neonates for the first 28 days showed essentially no differences in TEWL, hydration, skin surface pH and clinical observations. Skin hydration was raised in the cleanser arm at 14 days postnatal (ITT: mean wash score 49.7 (SD 9.2) vs water 46.7 (SD 8.4), p = 0.02, 95% CI −5.46 to −0.43), but was equal to those in the water group at 28 days postnatal.

There have been no studies to support the routine use of antiseptics. The once-conventional use of antimicrobial cleansers for routine infant bathing diminished following recognition of the toxicity risks. Hexachlorophene was widely used prior to 1975, and was subsequently associated with serious adverse reactions in infants, including fatal neurotoxicity. There has been only one subsequent report of an infectious complication possibly linked to a change in bathing with nonantiseptic cleanser. The other significant problem with any form of antiseptic is that it can interfere with the acquisition and evolution of normal flora, which may influence colonization with pathogenic bacteria and/or fungi.

Care of the infant scalp and hair follows the same principles as skin care. The same or similar gentle liquid cleansers may be used. ‘Baby’ shampoos are distinguished by a low ocular irritation index and a pH and saline concentration similar to those of tears. This is achieved by using very mild surfactant complexes and buffers in a similar approach to body wash products. Allergic contact dermatitis from cleansing products, including shampoos, is rare, as they have very brief contact with the skin before being rinsed off.

Minimal nail care is needed in the neonatal period. Fingernails should be trimmed to limit self-inflicted excoriation, avoiding close trimming that can cause bleeding and lead to infection.