Associations between sunlight exposure, skin pH and epidermal permeability in pregnancy

Author Identifier

Rachel Stevens

Date of Award


Document Type



Edith Cowan University

Degree Name

Master of Medical and Health Science by Research


School of Medical and Health Sciences

First Supervisor

Claus T Christophersen

Second Supervisor

Debbie Palmer

Third Supervisor

Shelley Gorman

Fourth Supervisor

Diana Arabiat


Maternal physiology, body composition, diet, and lifestyle during pregnancy are all intrinsically linked to the health of the developing child. However, recent studies have indicated that the skin barrier plays an important role in immune reaction. It has been established there is an increased risk of childhood sensitisation to normally benign allergens when there is epidermal barrier dysfunction. A breakdown of maternal epithelial junctions can allow allergens to enter the body and elicit immune responses that may in turn trigger potentially life-threatening reactions. Dysfunctional epithelial barriers may be a result of changes in skin surface pH and epidermal permeability. Increased sub-erythemal sun exposure may be one factor that can strengthen the maternal epidermal barrier preventing sensitisation and allergic diseases.

The objectives of this pilot study (SunPreg) were to increase the understanding of the changes occurring over time in the maternal skin barrier when exposed to UVR in the form of natural sunlight during pregnancy at different times of the year. Through the measurements of transepidermal water loss (TEWL) and skin surface pH, and sun exposure patterns, changes in epidermal permeability at various stages of the second half of pregnancy were examined. This study also explored relationships observed with maternal obesity and skin barrier.

SunPreg recruited a total of 50 pregnant women at 18-24 weeks of gestation and participants continued in this study until 36-38 weeks of gestation. At all three time points (18-24, 28-30, 36-38 weeks’ gestation), participants completed a validated sun questionnaire, and markers of skin integrity (TEWL and skin pH) were measured on the volar forearm. Fitzpatrick skin typing, self-reported daily sun exposure for the previous 7 days, use of sunscreen and sun avoidance behaviours (clothing), as well as recent sunburn history were also collected at each timepoint. Participants height and body weight were also measured.

Following 7 days of sun exposure, there was a significant decrease in TEWL at 28 weeks’(p < 0.01), but not at 20- or 36-weeks’ gestation. Similarly, a significant increase was found in skin pH at 28 weeks’ (p < 0.001) than at 20- or 36-weeks’ gestation. An inverse relationship of TEWL and skin pH was detected at 28 weeks’ gestation. Contrary to prediction, there was no significant association of Fitzpatrick skin types or seasons (summer and winter) with repeated measures of TEWL after adjusting for covariates. Yet skin types had significant mean differences for repeated measures of skin pH (p < 0.03). However, pre-pregnancy BMI had a significant positive association on repeated measures of TEWL (p < 0.001) but not skin pH.

Sun exposure was positively associated with increased TEWL at 20- weeks’ gestation (p < 0.01). However, there was a significant decrease in TEWL after sun exposure in summer, but not in winter (p < 0.01). Interestingly, increased pre-pregnancy BMI was associated with increased TEWL at 20-weeks’gestation (p < 0.004). However, Fitzpatrick skin types did not affect 20-week TEWL. Conversely, skin pH did not have significant main effects or interactions from any covariates at 20-weeks’ gestation.

These results suggest that epidermal permeability and skin pH fluctuates throughout pregnancy, especially at 28 – 30 weeks’ gestation. Another area of noted interest is the positive correlation between skin permeability barrier measurements and overweight/obesity. This supports previous evidence linking obesity with higher TEWL measurements and suggesting the epidermal permeability barrier is compromised by a higher weight. It also demonstrated skin pH readings differed with skin colour, supporting that skin pigmentation does influence epidermal pH following recent sun exposure.

Future research needs to expand upon the implications to both the mother, and her developing child, as a consequence of reduced skin barrier function during pregnancy as that is beyond the scope of this thesis.

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