When are moist applications helpful for nipple pain and what is moisture associated skin damage?

What do the terms moisture-associated skin damage, maceration and overhydration mean in guidelines for the healing of human skin wounds?

What is maceration?

Sustained exposure to moisture has been shown in various studies to result in overhydration. The term "macerated" has been used to describe the condition of skin subject to extended hydration. Maceration lacks a clear definition, though researchers agree that macerated skin is pale and soft. Its connective tissue fibres separate easily causing skin breakdown.

When skin is macerated

• Both epidermal and dermal hydration increase

• The pH of macerated skin becomes more alkaline than healthy skin.

Pathophysiologically, maceration

• Alters permeabiity and flexibility of the stratum corneum

• Weakens intercellular attachment, and

• Changes electrical impedance properties

As a result, a macerated epidermis is more vulnerable to mechanical pressure. In chronic exudative wounds, high levels of peri-wound maceration delay healing.1 3 4

What is moisture-associated skin damage?

Maceration is just one component of what is most recently referred to as moisture associated skin damage (MASD), though there is also no agreed definition for MASD. MASD is a term used in wound care literatures and guidelines for visible skin inflammation and damage caused by prolonged exposure to a source of moisture.

MASD presents as

• Erythema

• Maceration, or

• Skin erosion.

In the presence of overhydration of the skin (whether macerated or not), MASD is triggered by mechanical forces such as

• Friction

• Shearing

• Stretching.

In the presence of overhydration, MASD is also triggered by irritants, which may be

• Microbial or

• Chemical.

Why has moist wound healing become so popular?

Shortly after I was born, Dr George Winter compared the effect of leaving superficial wounds exposed to form a scab with the application of a vapour-permeable film dressing on 12 young domestic pigs. Dr Winter found that the pigs' wounds healed twice as quickly in the first three days when kept humid.5 From Day 7 there was no difference between both groups. Nevertheless, from then on, throughout my life-time, moist wound healing increasingly became the standard 'evidence-based' approach to human skin wound healing, with this study frequently cited as foundational evidence.

Subsequent to Dr Winter's seminal experiment, moist wound healing has been extensively studied for burns and skin grafts, and for chronic wounds due to blood circulation insufficiencies such as pressure sores, venous insufficiency, diabetic ulcers, and neuropathies, demonstrating benefit for these conditions. However, these conditions are radically different, in multiple ways, to the wounds that develop in the lactating nipple.

In the moist wound healing approach, a dressing controls hydration and holds moisture on a wound surface. A dressing is dry if there isn’t any medium to absorb and contain the extracellular fluid and matrix.

• Today, bio-occlusive dressings are designed to act as membranes which let oxygen in, yet retain a moisture balance so that the wound is neither too dry nor too moist. This promotes faster wound healing with less scar in the contexts of burns, skin grafts, and chronic wounds.

• Classic wound care also requires removal of necrotic and non-viable tissue, slough, bacteria, exudate, deleterious cytokines, debris – known as debridement.

Pathophysiological mechanisms

Moist wound healing aims to stop the formation of a solid, impenetrable scab, made of dehydrated and dead cells. Scab healing slows down wound healing in the context of burns, skin grafts and the chronic wounds of chronic disease, because

• Scabs slow down the migration of fragile new epithelial (or keratinocyte) cells across the base of the wound through the exudative layer

• Moist wound healing promotes more capillary formation, to bring in nutrients and healing factors. Better activation of cytokines and growth factors promotes less wound contracture and more re-epithelialisation, with less pain and scarring.

Relevant findings about human skin and moisture in general

• Water content is already as high as 70% in a healthy epidermis.

• Continuous exposure of human skin to water for 72-144 hours results in a mild, transient dermatitis or eczema in half of skin test sites.1

• Corneocytes swell with prolonged exposure to water, though their network of keratin filaments limits how much can be absorbed.2

• Hyper-hydration causes desmosome rupture, microstructural changes in lipid self-assembly, and penetration of biomacromolecules through the barrier of the stratum corneum. Hyper-hydration also penetrates into the dermis.

• Extended hydration and swelling of the corneocytes results in increased epidermal thickness, dilation of intracellular spaces, enhanced mitotic rate, and reduced cytokine levels.

• The temperature of wet skin is lower.

• The vascular perfusion of wet skin is higher.

• Wet skin is more vulnerable to mechanical pressure.

Relevant findings about moist wound healing and human skin

• In one important 2016 study of skin (from a woman’s breast but not during lactation), researchers found that at 7% relative humidity, the sheer crack plane was aligned with the direction of the stress. At 100% relative humidity, the cracks were longer, with increased area of crack interface, and an increased energy cost of tissue rupture.2

• The formation of a dry scab has been shown to inhibit bacterial growth and displace most of the bacterial burden away from the wound bed, leading to decreased levels of inflammation in a skin wound, and allowing faster granulation tissue formation.

• Whitehead et al showed that healing skin with less moisture contact is more comfortable, overall, and argued that patient comfort has not been properly assessed in moist wound healing. Whitehead et al propose that although moist wound healing is important in certain contexts, the risks of overhydration are significant, resulting in pain and discomfort, which is clinically significant and is as important as reducing the healing time.1 (Whitehead et al raise this concern about skin healing generally - in the absence of the added complication of a covering nursing bra.) '

• Moist wound healing fails to consider the role of granulation in the management of exuding wounds, which is relevant to the unique environment of the lactating nipple.3

• Scab wound healing is known to decrease risk of infection compared to moist wound healing. Scab formation is part of the normal healing of an acute wound, and results in healing without infection even though epithelialisation may be slower relative to moist wound healing.

• A 2016 study of 10 rabbits’ ears showed that desiccation of acutely generated wounds improved wound healing, with decreased bacterial burden in the wound bed, increased granulation tissue formation, and less up-regulation of inflammatory markers compared to saline-treated wounds.6

• Some researchers have begun to question the orthodoxy of moist wound healing, arguing that semi-permeable moist wound healing may be beneficial in certain contexts, such as chronic wounds, burns and grafts, but that this is not always the case. The benefits of the hyperosmolar environment which develops during desiccation and scab formation is acknowledged to outweigh the benefits of rapid epithelialization in certain settings.

NDC Clinical Guidelines argue that there are benefits to the hyperosmolar environment of dessication and scab formation in the case in lactation-related nipple pain and damage, due to the unusual and unique risk of overhydration and MASD of the lactating nipple-areolar complex, and the NAC's unique repetitive exposure to vaccum and other mechanical forces.

Selected references

Douglas PS. Re-thinking lactation-related nipple pain and damage. Women's Health. 2022;18:17455057221087865.

Liu X, Cleary J, German GK. The global mechanical properties and multi-scale failure mechanics of heterogeneous human stratum corneum. Acta Biometerialia 2016;43:78-87.

Nozimotor IN, Da Silva BA, Bandeira MD. Nonpharmacological interventions for treating breastfeeding nipple pain: systematic review and meta-analysis. Breastfeeding Medicine. 2024;19(8):DOI: 10.1089/bfm.2024.0043.

Nguyen JK, Huang A, Siegel DM, Jagdeo J. Variability in wound care recommendations following dermatologic procedures. Dermatologic Surgery. 2020;46(2):186-191.

Savas EH, Tumkaya MN, Semerci R, Eroglu K. Comparison of the effect of natural products and breast milk for preventing and treating nipple trauma and pain in lactating women: a systematic review and meta-analysis. Explore. 2024;20:103019.

Conde-Montero E, Moreau A, Schlager JG, Pastor D, Hafner J. Protocols in wound healing: evidence-based or mere rituals? International Wound Journal. 2024;21:e70062.https://doi.org/70010.71111/iwj.70062.

Citations

1. Whitehead F, Giampieri S, Graham T, et al. Identifying, managing and preventing skin maceration: a rapid review of the clinical evidence. Journal of Wound Care 2017;26(4):159-65.
2. Drago F, Gariazzo L, Cioni M. The microbiome and its relevance in complex wounds. European Journal of Dermatology 2019;29(1):6-13.
3. Rippon MG, Ousey K, Cutting KF. Wound healing and hyper-hydration: a counterintuitive model. Journal of Wound Care 2016;25(2):68-75.
4. Oousey K, Cutting K, Rogers AA. The importance of hydration in wound healing: reinvigorating the clinical perspective. Journal of Wound Care 2016;25(3):122-30.
5. Winter G. Formation of the scab and the rate of epithelization of superficial wounds in the skin of the young domestic pig. Nature 1962;193:293-94.
6. Park E, Long SA, Seth AK, et al. The use of desiccation to treat Staphylococcus aureus biofilm-infected wounds. Wound Repair and Regeneration 2016;24:394-401.
7. Taudorf EH, Jemec GBE, Hay RJ, et al. Cutaneous candidiasis - an evidence-based review of topical and systemic treatments to inform clinical practice. Journal of European Academy of Dermatology and Venereology 2019;33:1863-73.
8. Cable B, Stewart M, Davis J. Nipple wound care: a new approach to an old problem. Journal of Human Lactation 1997;13(4):313-18.
9. Brent N, Rudy SR, Redd B, et al. Sore nipples in breast-feeding women: a clinical trial of wound dressings vs conventional care. Archives of Pediatric and Adolescent Medicine 1998;152(11):1077-82.
10. Dodd V, Chalmers C. Comparing the use of hydrogel dressings to lanolin ointment with lactating mothers. Journal of Obstetric, Gynecologic, and Neonatal Nursing 2003;32(4):486-94.
11. Mohammadzadeh A, Farhat A, Esmaeily H. The effect of breast milk and lanolin on sore nipples. Saudi Medical Journal 2005;26(8):1231-34.
12. Dennis C, Jackson K, Watson J. Interventions for treating painful nipples among breastfeeding women. Cochrane Database of Systematic Reviews 2014(12):doi:101.1002/14651858.CD007366.pub2.
13. Sasaki BC, Pinkerton K, Leipelt A. Does lanolin use increase the risk of infection in breastfeeding women? Clinical Lactation 2014;5(1):28-32.
14. Jackson KT, Dennis C-L. Lanolin for the treatment of nipple pain in breastfeeding women: a randomized controlled trial. Maternal and Child Nutrition 2017;13(3):e12357.
15. Neto CM, De Albuquerque RS, De Souza SC, et al. Comparative study of the use of HPA lanolin and breast milk for treating pain associated with nipple trauma. Rev Bras Ginecol Obstet 2018;40(11):664-72.
16. Abou-Dakn M, Fluhr JW, Gensch M, et al. Positive effect of HPA lanolin versus expressed breastmilk on painful and damaged nipples during lactation. Skin Pharmacol Physiol 2010;2011(24):27-35.
17. Bourdillon K, McCausland T, Jones S. Latch-related nipple pain in breastfeeding women: the impact on breastfeeding outcomes. British Journal of Midwifery 2020;28(7):406-14.