Baby Skin Anatomy and Its Role in Diaper Development

Summary

If we assume the average human lifespan is 70 years, it is clear that human skin is exposed to various environmental conditions throughout this period and demonstrates extraordinary adaptation to these conditions. The role of our skin is quite significant in performing critical functions such as preventing water loss in the skin, maintaining constant body temperature, and protecting the body against all kinds of threats from outside. Particularly during infancy, skin undergoes numerous changes, and because the skin structure and barrier properties of babies are not fully developed compared to adults, infants require extra care during their care routines. This study discusses infant skin anatomy and the factors affecting the skin, as well as factors to be considered in studies on infant diapers.

Skin Anatomy

The skin is the body's largest organ, comprising 15% of an adult human's weight. In addition to providing protection against any physical, chemical, or biological hazards from outside, it has vital functions such as preventing excessive water loss from the body and maintaining body temperature. Human skin consists of three layers from outside to inside: the epidermis, dermis, and subcutaneous tissue. The thickness of these skin layers varies depending on their location in the body. For example, while the thickness of the eyelid, which has the thinnest epidermal layer in the body, is measured at less than 0.1 mm, the thickness of the epidermal layer of the palm or sole of the foot has been measured at approximately 1.5 mm [1].

Stratum Corneum Layer

Human skin acts as a barrier between the body and the external environment. The stratum corneum (SC) structure, located in the outermost layer of the skin, fulfills this barrier function. The stratum corneum layer has critical functions such as preventing excessive fluid loss from the epidermis and protecting the body against harmful compounds that may enter from the external environment. The stratum corneum layer is composed of cholesterol, free fatty acids, and ceramides [2]. The stratum corneum is a lipophilic structure with very high water impermeability that protects inner layers from environmental effects. In fact, the skin's barrier function varies according to age and external factors (humidity, temperature, etc.). For example, after age 20, the amount of hyaluronic acid (HA) present in human skin gradually decreases, and as a result, skin elasticity and the amount of water retained in the skin decrease, and wrinkles begin to form. When the amount of water in the skin falls below the skin's normal moisture level (20–35%), the skin dries, hardens, becomes scaly, reddish capillary cracks or itching may occur [3].

Infant Skin Anatomy Newborn Infant Skin Anatomy

Birth can be cited as the best example of adaptation shown by human skin to environmental conditions. In the face of such a sudden event, a newborn infant survives with the oxygen provided by the mother and completes its development in a water-filled container at 37°C temperature, while within minutes transitioning to a cold, dry, terrestrial environment and actively begins breathing with its lungs. Consequently, the skin undergoes considerable changes during this period. The epidermis layer of infant skin reaches full maturity between weeks 30-37 of pregnancy. Although the formation of the stratum corneum (SC) layer is completed in the last 3 months of pregnancy, even within a year after birth it does not possess protective properties as strong as adult skin. Therefore, the table showing functional, structural, and biological differences between infant skin and adult skin, which have different characteristics from each other, is as follows [2]. Until the age of two, the thickness of the epidermis layer in infants' skin is 20% thinner than in adults; the stratum corneum layer is 30% thinner [2]. During the last 3 months of the time infants spend in the womb, their skin is additionally covered with a protective substance called vernix caseosa, which has a white, cheese-like appearance and lipophilic (fat-loving) structure that aids in the maturation of the epidermal layer within the uterus and after birth [4]. Generally, when babies are first born, they are bathed to remove this creamy, thick layer. However, when washed, much of this layer is wiped away. In newborns who are not bathed after birth, it has been found that skin rashes commonly encountered in the neonatal period occur less frequently. Additionally, the World Health Organization recommends that infants not be bathed within the first 6 hours after birth [5].

Premature Infant Skin Anatomy

Because the stratum corneum layer forms in the last 3 months of pregnancy, the epidermis layer in the skin of prematurely born infants has not fully developed, and the thickness of the stratum corneum layer varies depending on the stage of prematurity. High transepidermal water loss (TEWL) is expected in premature infants. The table below shows TEWL values for the fetus developing within the womb based on time. As can be seen from Figure 3, there is a gradual decrease in TEWL values from week 24 until weeks 33-34. Therefore, particularly in premature infants born earlier than weeks 34-40, TEWL values are higher compared to fully developed infants, which means that premature infants' skin is more sensitive and more prone to infection [6]. Because infants lack the ability to control their urine and feces, appropriate hygiene conditions in the genital area and certain preventive measures for skin protection are necessary. Therefore, the use of absorbent infant diapers is quite important for maintaining hygiene. To meet the needs of parents and caregivers and support infant development, it is necessary to deeply understand skin anatomy and biochemistry so that infant diaper products are sustainable and innovative [4]. Therefore, starting with processes in the womb and continuing through birth and numerous subsequent changes, the biophysical measurements of changes affecting the skin can be listed as transepidermal water loss (TEWL), skin hydration, and skin pH value.

Transepidermal Water Loss (TEWL)

TEWL measurement is the most effective way to understand the functional condition of epidermal tissue. It refers to the amount of water lost from a specific skin area within a specific period (g/m2/hour or day). It is used to measure water loss from epidermal tissue [6]. The TEWL method is quite important for understanding whether the diaper keeps the baby's skin dry by measuring the barrier condition of the skin in the diapered area or water loss from the skin surface (TEWL) [4].

Skin Hydration

One of the important functions of the skin is preventing dehydration and ensuring the preservation of body fluids. When the 10% water content necessary for the skin to feel moist decreases, dryness occurs. As moisture in the external environment decreases and evaporation increases transepidermal water loss, it is compensated by epidermal and dermal tissues, and maintaining continuous moisture is important. Newborn skin has a relatively drier structure compared to older infants [7].

Skin pH

At birth, the newborn skin surface has neutral or alkaline pH (pH: 6.2-7.5). In both term and preterm infants, skin pH decreases rapidly within the first week following birth and then more slowly over the following 3 weeks. By the end of the first month, they acquire a pH value very close to adult skin pH (pH: 5.0-5.5). As skin pH shifts toward acidity, it contributes to skin integrity, supports epidermal innate immunity, and reduces pathogenic bacterial colony counts. Therefore, the pH value of infant skin is of critical importance [8]. As shown in Figure 4, materials such as water, wet wipes, and infant diapers used to maintain hygiene in the infant's diaper area damage fatty acids in the stratum corneum layer in certain circumstances, thereby compromising skin integrity. Enzymes found in the infant's urine or feces enter through the compromised stratum corneum layer and break down proteins there. These enzymes penetrate the fibrous sections in lower skin layers and completely permeate the epidermis layer, causing problems such as inflammation and diaper rash. In addition to the materials mentioned above, other causes that may lead to diaper rash include antibiotic use during infant teething, the introduction of solid foods in 6-12 month-old infants, diarrhea or digestive system problems, the infant consuming acidic foods such as oranges and mandarins, inadequate drying of the skin after wet wipe use or sweating, the diaper remaining on the infant for a long time leaving the skin airless, and infrequent diaper changes. In fact, the replacement of reusable cloth diapers with cellulose disposable diapers, followed by the use of highly absorbent superabsorbent polymer (SAP) material and breathable outer surfaces, has been shown to significantly reduce diaper rash problems [8].

Conclusion

In the study conducted, the skin anatomy of infants and adults was examined and the differentiated points in skin characteristics were compared. Given these findings and considering the sensitivity of infant skin compared to adult skin, the compatibility of work done or to be done on infant diapers with the skin and the performance of the finished product are of critical importance. Therefore, in studies to be conducted related to infant diapers, it is recommended to consider transepidermal water loss (TEWL), skin hydration, and skin pH values as quantitative measures of changes affecting the skin. Additionally, the research conducted has shown that diaper rash is not solely caused by infant diaper or wet wipe use but rather by factors such as infant illness, teething during infancy periods, or various foods consumed. Ezgi Sayınkaplan - Chemical Engineer, Senior Research and Development Engineer - Evyap Sabun Yağ Gliserin San. ve Tic. A.Ş.

References [1] Kolarsick, P., A., J., Kolarsick, BS, M., A., Goodwin, C., Anatomy and Physiology of the Skin, Chapter 1. [2] Agner, T., Skin Barrier Function, Current Problems in Dermatology, Vol.49, Karger. [3] Freitas, F., Vítor D. Alves, V. D., Reisa, M., A., M., Bacterial Polysaccharides: Production and Applications in Cosmetic Industry, Springer, 2014. [4] Adam, R., Skin Care of the Diaper Area, Pediatric Dermatology Vol. 25, Wiley, 2008. [5] http://www.abcderm.com.tr/?makale=yenidoganbebegin- özel-kremi-verniks (Last Accessed: 20 September 2019). [6] Fluhr, J., Elsner, P., Berardesca, E., Maibach, H., I., Bioengineering of the skin, Water and the Stratum Corneum, 2. Edition, CRC Press, 2005. [7] Karabulut, A., A., Skin Physiology in Newborns and Topical Drug Use, Türkderm, 2011. [8] Odio, M., Thaman, L., Diapering, Diaper Technology and Diaper Area, Skin HealthPediatric Dermatology Vol. 31, 2014.