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Impact of Urine on Diapered Skin Health

Suhyoun (Su) Chon, PhD, and Ben Minerath, MS, Kimberly-Clark Corp., 2016

Summary

A recent survey on baby wipe use revealed that, surprisingly, some caregivers do not clean

diapered skin if the diaper change involves the presence of urine only (Furber et al., 2012).

In this review, the impact of urine exposure to baby skin is revisited to highlight the

importance of good skin hygiene practice for maintaining healthy baby skin. First, basic

knowledge of urine composition and unique properties of baby skin are reviewed to

describe how urine interacts with and impacts baby skin. Then, potential harmful effects of

specific urine constituents and the benefits of using appropriately formulated baby wipes

are discussed in detail.

Proper hygiene practice in diapered skin has been well recognized as essential for

maintaining healthy baby skin. In particular, the effective removal of urine and feces from

baby skin is necessary to maintain intact skin barrier against external irritants, thus,

minimizing the incidence of diaper rash (Hopkins, 2004). In a recent survey on diaper area

cleansing, it has been found that some parents do not clean baby skin after urination alone

(Furber et al., 2012). Although the combination of both feces and urine causes the most

severe skin damage (Atherton, 2001; Buckingham et al., 1986), urine itself is sufficient to

trigger skin irritation as well (Berg et al., 1986). Potential irritation factors of residual urine

on baby skin will be reviewed and the benefit of appropriate skin cleansing of the diapered

area will be revisited in this article to help inform diapering practices that promote healthy

baby skin.

Background: Urine and Baby Skin

Bladder functions of newborns are not mature at birth and continue to develop throughout

infancy (Sillén, 2001). The frequency and volume of urination change as their bladder

maturity and capacity increases (Sillén et al., 2004). Detailed metrics on bladder capacity

and frequency of urination during infancy are described in Table 1. In general, babies

normally urinate 15-20 times per day with an average void volume around 60 mL during

the first year of their life (Deborah M et al., 2016; Sillén et al., 2004).

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Table 1: Bladder capacity and urination frequency during infancy

Age Bladder Capacity (mL) Urination Frequency per Day

Pre-term baby (32 weeks) 12 22-24 times

Full term baby 50 22-24 times

1 year old 70 12-15 times

2 years old (pre-potty trained) 70 12-15 times

3 years old (post-potty trained) 120 3-7 times

Modified from Sillén et al, 2004

Figure 1: Composition of human urine

Much is known about the composition and properties of human urine both in health and

disease. The composition of human urine is mostly water (95%) while the remaining

constituents are urea, uric acids, salts (Na, K, Cl, P) and trace amounts of hormones and

metabolites (Rose et al., 2015) (Figure 1). Interestingly however, advanced analytical

technologies have recently been applied to urine analysis that enabled the identification of

more than 3000 metabolites in human urine (Bouatra et al., 2013), suggesting new insights

on urine composition and impact on skin health. The normal pH of urine from healthy

babies and adults is neutral to slightly acidic, typically ranging between pH 6-7 (Rose et al.,

2015). The physiological ranges for urine osmolality have been reported to be 50 mmol/L

to 600 mmol/L in pre-term and 800 mmol/L in full term babies (Modi, 1999).

Although basal skin barrier function of healthy full term babies seems to be competent for

survival in a terrestrial environment at birth, physical properties of infant skin is quite

different from adults as summarized in Table 2. The size (volume and surface area) of

corneocytes from baby skin is 20% smaller than those derived from adult skin and stratum

corneum was found to be 30% thinner than in adults. Corneocytes are dead skin cells that

normally reside within the outermost layer of the skin, the stratum corneum. They play a

Water95%

Urea2%

Inorganic Salts (Na, K, Cl and P),

Hormone and Other Metabolites

3%

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key role in providing the skin’s barrier function which largely resides in the stratum

corneum. Infant skin has higher surface pH especially in newborns, lower sebum secretion,

and higher transepidermal water loss (TEWL) a measure of skin barrier function; higher

values often indicate lower barrier properties (Telofski et al., 2012). However infant skin

continues to mature especially during the first year of life. For example, acid mantle

formation in skin, which plays a pivotal role in barrier augmentation, rapidly develops

during the first month after birth (Fluhr et al., 2010 and Telofski et al., 2012). Finally, it is

clear that the skin microbiome evolves considerably in parallel with skin maturation

following birth (Capone KA et al., 2011). Taken together, these intrinsic factors result in

baby having less resilient skin barrier function compared to that of adults (Telofski et al.,

2012).

Table 2: Different characteristics of baby skin vs. adult skin

Characteristics Baby Skin Adult Skin

Epidermis

Corneocytes (surface area & volume) Small Large

Stratum Corneum Thickness Thin Thick

Pigmentation Less More

Natural Moisturizing Factor Less More

pH High (first month) Low

Sebum Less More

Transepidermal Water Loss High Low

Dermis

Collagen fiber density Less More

Papillary-to-reticular dermis transition Not clear Clear

Modified from Telofski et al., 2012

In addition to these intrinsic properties, diapered baby skin is frequently exposed to various

extrinsic challenges during diaper wear. The main risk factors for diaper dermatitis include

1) over-hydration 2) mechanical friction and 3) urine and fecal derived skin irritants

(Atherton, 2001; Andersen et al., 1994; Berg et al., 1994). In particular, over-hydration

caused by prolonged urine exposure results in the outermost layers of the skin (stratum

corneum) softening and weakening (maceration), thereby making the skin more susceptible

to physical damage (i.e. friction) and irritant penetration (Atherton, 2001). Warner et al.

demonstrated how over-hydration disorganized the physical barrier structure of skin using

transmission microscopy (Warner et al., 2003). A simplified illustration describing those

changes is provided in Figure 2, which includes 1) swelling of corneocytes 2) abnormal

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formation of large pools of water in intercellular spaces 3) disrupted intra-corneocyte lipid

bilayer structure and 4) degradation of corneodesmosomes which are the inter/intra-

cellular structures required for corneocyte adhesion (Warner et al., 1999 and 2003). In

addition to these structural changes, clinical data suggest that increased skin pH is

positively correlated with skin wetness (Berg et al., 1994). Indeed, Sun et al. also found this

correlation in an in vitro skin equivalent culture (Sun et al., 2015), suggesting that high

humidity may disturb acid mantle formation in skin. This is important because acid mantle

formation plays a critical role in maintaining intact barrier function. Moreover, increased

skin pH is known to promote the growth of harmful microorganisms, including Candida

albicans, Staphylococcus aureus, and various streptococci (Ness et al., 2013). Finally it has

been shown that high humidity itself can alter the population of skin microflora (McBride

et al., 1977).

Figure 2. Skin barrier disruption caused by over-hydration

Taken together, relative to adults, baby skin is more susceptible to the intrusion of

pathogens and various irritants due to both intrinsic properties and extrinsic challenges

(Berg et al., 1994; Wilhelm et al., 1990). Therefore, diaper area cleansing should be effective

enough to remove potential irritants but gentle enough not to perturb intact skin barrier.

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Diapered area cleansing following urination: importance and benefits

Removing potential skin irritants in urine

The role of urine alone as a skin irritant is, to be sure, less likely to be a critical element of

diapered skin irritation when compared to the irritancy associated with exposure to feces

or urine and feces combined (Atherton, 2001; Andersen et al., 1994; Buckingham et al.,

1986). However, it seems equally clear that the presence of urine components is not benign

to skin health. Berg et al. have explored the role of urine in the development of diaper

dermatitis and found that urine itself increases the permeability of diapered skin to irritants

and can directly irritate skin when exposure is prolonged (Berg et al., 1986). This harmful

effect was not due to over-hydration since the defect was significantly higher than water

exposure (Table 3), suggesting certain components in urine accelerated barrier damage in

skin. The underlying mechanism remains elusive, but perhaps inorganic salts present in

urine may alter electrolyte balance in skin, thereby eliciting barrier damage. Thus, it seems

apparent that if skin cleansing is not done properly following each diaper change, an excess

amount of salts may accumulate on the skin’s surface eventuating in elevated

transepidermal water loss (TEWL), an indication of compromised skin barrier integrity.

Table 3: Skin permeation following water or urine exposure

Treatment Permeation of 3H2O

(CPM; Mean ± SD)

Occlusion only 12,975 ± 5,900

Water 17,563 ± 5,414

Baby urine 290,245* ± 24,600

Modified from Berg et al. 1986, *p ≤ 0.05 vs other treatments. Hairless mice were patched with baby urine, water, or dry

patches. Following 10 days of exposure, the area of skin was excised and placed on a penetration chamber as described

by Cooper et al. Permeability of the skin was determined by measuring the penetration of a tracer molecule (3H2O)

through the skin.

Except water, urea is the most abundant component (2%) in urine. It has been suggested

that urea alone does not trigger significant skin irritation (Berg et al., 1986). However,

feces, a source of the enzyme urease, promotes the production of ammonia from the urea

present in urine. Thus, concurrent or subsequent exposure of urine contaminated skin to

feces will hydrolyze urea to ammonia, increasing skin pH and damage the skin. Thus, the

prompt removal of urine from the skin should help to maintain the ideal pH of diapered skin.

The composition of the remaining 3% of urine (that is beyond water and urea) seems to be

much more diverse than previously thought. As mentioned earlier, Bouatra et al. have

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identified more than 3000 metabolites in human urine in their recent metabolomic study

(Bouatra et al., 2013). Chemical subclasses and the number of metabolites in each category

are described in Table 4. Given that urine is 95% water by weight, and accordingly is

hydrophilic in nature, it is surprising to see that 866 different lipid molecules (hydrophobic)

are present in urine. Also trace amounts of bile acids are found as well (Bouatra et al., 2013).

It is interesting to speculate whether the presence of these trace metabolites will affect

diapered skin health. Further research opportunities seemingly exist to explore this

hypothesis.

Eliminating odor

Residual urine on baby skin often produces unpleasant odors derived from the breakdown

of urea to ammonia and other volatile constituents as well. Thus thorough skin cleaning is

necessary not only for promoting skin health, but also for reducing the presence of odors

that can emanate from baby skin.

Table 4: Chemical classes in a urine metabolome database

Chemical Class # of Compounds Identified

Aromatic Compounds 1233

Lipids 866

Amino Acids, Peptides, and Analogues 286

Aliphatic Acyclic Compounds 199

Carbohydrates and Carbohydrate Conjugates 116

Organic Acids and Derivatives 108

Polyketides 74

Nucleosides, Nucleotides, and Analogues 49

Alkaloids and Derivatives 45

Homogeneous Metal Compounds 45

Others 58

Modified from Bouatra et al. (2013) The Human Urine Metabolome. PLoS ONE 8(9): e73076

Providing proactive skin care using appropriately formulated baby wipes

Proper skin cleansing during diaper changes will not only remove potential irritants

effectively, but can also provide additional skin protection from subsequent exposures to

feces (Ness et al., 2013). Despite the common perception, many clinical studies have

demonstrated that usage of pre-moistened commercial baby wipes is safe and furthermore

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performed better on maintaining healthy baby skin, when compared to water only

cleansing regimens (Ehretsmann et al., 2001, Lavender et al., 2012 and Visscher et al., 2009).

Potential benefits of disposable wipe use have been discussed in several reviews (Stamatas

et al., 2014; Blume-Peytavi et al., 2014) and the important skin health attributes identified

include 1) effective removal of skin irritants, 2) balancing physiological skin pH, and 3)

applying emollients to protect baby skin from friction and subsequent exposures to urine

and/or feces. Cunningham et al. have discussed the importance of baby wipe formulation

development and suggested that the ideal compositions will provide skin care benefits to

sensitive baby skin (Cunningham et al., 2007 and 2009). For example, aqueous solutions

used in baby wipes are usually formulated to have a final pH in the range of 4.5-6.5 and

provide a buffering capacity to balance skin surface pH, thereby augmenting barrier

integrity (Cunningham et al., 2007 and 2009). Emollients often formulated in baby wipes

such as behenyl alcohol, stearyl alcohol, stearic acid and triglycerides could also help care

for baby skin by providing lipid-like properties, protecting skin surface from excessive

hydration and harmful insults (Cunningham et al., 2009). Therefore, baby wipe use after

urination should be strongly encouraged, not only for cleansing purposes (removing

irritants and preventing bad odor), but also to provide proactive skin care protection in

anticipation of subsequent exposures to feces.

Conclusion

Prolonged skin exposure to urine and feces is the main cause of diaper dermatitis. It has

been reported that 50% of babies experience this inconvenient skin irritation at some point

during the first year of life (Atherton, 2001). It seems that the incidence and severity of

diaper rash can effectively be reduced by consistently practicing optimal hygienic practices

at each diaper change. Urine exposure can significantly disturb baby’s sensitive skin,

disorganizing barrier structure of the upper most layer of the skin (stratum corneum),

altering skin pH and composition. Potential harmful effects from residual inorganic salts

and other compounds, including those recently identified in the technical literature, cannot

be excluded. Removing sources of odor from baby skin is another obvious reason in

addition to all the skin health aspects discussed above. Thus, thorough skin cleansing using

gentle pre-moistened baby wipes is strongly recommended following each diaper change

as part of an optimal skin care regimen.

Acknowledgement

We would like to thank Karien Rodriguez for her thoughtful guidance on the paper.

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