Fluctuations in equine cutaneous pH and transepidermal water loss with time of day and ambient conditions.
Authors: Discepolo D R, Gaare E, Handlos G, Perry E B
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Equine Skin Barrier Function Varies Predictably Throughout the Day Researchers measured cutaneous pH and transepidermal water loss (TEWL)—two key indicators of skin barrier integrity—across five anatomical sites in nine mares over five consecutive days at three-hourly intervals (6 AM, 12 PM, 6 PM), whilst simultaneously recording ambient temperature and humidity. Cutaneous pH fluctuated significantly both between days and across the day (with neither pattern dependent on anatomical location), whereas TEWL showed more pronounced variability, differing significantly by day, time of measurement, and body region; notably, all TEWL measurements correlated strongly with environmental temperature and humidity (P < 0.0001), whereas pH remained independent of these ambient conditions. These findings indicate that standardising measurement protocols—particularly accounting for time of day and environmental conditions—is essential when using TEWL as a dermatological research parameter in horses, though pH appears more stable across conditions. For practitioners conducting objective skin assessments or comparing results between cases, timing and environmental conditions warrant consideration, especially when evaluating horses with barrier dysfunction or dermatological disease where TEWL measurements might be relied upon for diagnostic purposes.
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Practical Takeaways
- •When measuring equine skin barrier function for clinical or research purposes, standardize measurement time of day and record ambient temperature/humidity, as TEWL varies significantly with these factors
- •Environmental conditions substantially influence transepidermal water loss but not cutaneous pH in healthy horses, so temperature and humidity control is critical for consistent dermal assessments
- •Multiple anatomical locations should be sampled when assessing TEWL due to significant regional variation, though pH measurements may be more stable across body sites
Key Findings
- •Cutaneous pH significantly varied by day (P = 0.0052) and time of day (P = 0.0073), with a significant day-location interaction (P = 0.0004)
- •TEWL significantly differed by day (P < 0.0001), time (P < 0.0001), and anatomical location (P = 0.0231), with three-way interaction of day, time, and location (P = 0.0167)
- •TEWL across all locations showed significant correlation with temperature and humidity (P < 0.0001), whereas pH showed no significant associations with environmental conditions
- •Anatomical location did not affect mean cutaneous pH (P = 0.2841) but significantly affected TEWL measurements