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Research notes

Cori Dog Research Note · version 1.1

Measuring canine skin: pH, water loss and hydration

Organization author · Cori DogStructured evidence map; no pooled estimate
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The short answer

What do surface pH, transepidermal water loss and hydration measurements represent in canine studies, and which sources of variation limit simple targets?

Canine skin pH, transepidermal water loss and hydration describe different features of the skin surface and barrier. They can be useful research measurements when method, body site and conditions are controlled, but no single reading is a diagnosis, a universal target or proof that a shampoo will suit a dog.

What should a skin measurement mean to you?

A number on a shampoo bottle and a reading taken from your dog's skin answer different questions. Use this note to understand what was measured before deciding what the result means.

  1. 1. First ask: a measurement of what?

    Was the number measured in the bottle, in diluted shampoo or on a dog's skin? Was it acidity (pH), water leaving the skin (TEWL) or moisture in the outer skin layer? Write down the name of the measurement alongside the number. A bare number leaves out the most useful part.

  2. 2. Then ask: what was it compared with?

    Two readings are easier to interpret when the body site, equipment and conditions match. For example, a result from an ear before a wash cannot be treated as a direct comparison with a result from the belly afterwards. Ask which conditions stayed the same and whether measurements were repeated.

  3. 3. Keep what you noticed separate from the explanation

    For a veterinary conversation, describe what you saw and when: for example, 'scratched the left side after the wash on Tuesday'. Keep the product label and the measurement report as context. Neither your observation nor a pH value, by itself, tells you the cause or which product is suitable.

For the quick explanation, read the four takeaways below. The study atlas is for comparing how individual studies measured skin; its numbers are not targets to test your dog against.

Why this matters

Numbers can look more certain than they are. A pH reading may change with body site, age, breed and measurement conditions. A water-loss reading can respond to deliberate barrier damage yet still vary substantially when repeated in ordinary study settings.

The useful question is therefore not whether one number is good or bad. It is whether the same endpoint was measured in a comparable way, whether uncertainty was reported, and whether the conclusion stays within what that endpoint can show.

Four takeaways

01

There is no single canine skin-pH target

Studies of healthy dogs report variation by age, anatomical site and breed. Their results are observations from particular populations and methods, not a pass-or-fail number for every dog.

Sources 1, 3, 2

02

The three measurements are not interchangeable

pH describes acidity at the measured surface, TEWL estimates water vapour leaving through the skin, and hydration instruments estimate water-related properties of the outer layer. One cannot substitute for another.

Sources 4, 2, 6

03

TEWL can be meaningful and still be noisy

Experimental barrier disruption can raise TEWL, showing biological relevance. Separate repeatability studies show that device, observer, site, day and dog can also change the reading. Controlled repeated comparisons are stronger than one isolated value.

Sources 6, 5, 4

04

Product pH is not a skin-response test

Commercial shampoos can have different measured pH and viscosity, but those measurements do not establish tolerance, barrier response or suitability. The finished formula and intended use still require their own evidence.

Source 7

Key terms, in plain language

Surface pH
A measure of acidity or alkalinity at the exact skin surface and moment tested. It is affected by site and method and does not describe the whole skin barrier.
Transepidermal water loss (TEWL)
An estimate of water vapour passing outward through the skin. Higher readings can accompany barrier disruption, but environmental and measurement variation must be controlled.
Stratum-corneum hydration
An instrument-based estimate of water-related properties in the outermost skin layer. It is not the same as whole-body hydration or a visual judgement of dryness.
Repeatability
How similar repeated readings are when the measurement is repeated under defined conditions. A repeatable measurement can still be non-diagnostic.

Worked example

Example: two readings from one healthy dog

A fictional study measures surface pH at an ear on one day and at the groin after a recent wash on another day. The values differ.

  1. 01

    The difference does not by itself show deterioration or improvement. Body site, recent washing, timing and measurement conditions all changed.

  2. 02

    A stronger comparison would repeat the same instrument at the same site after the same acclimatisation, with recent topical products and environmental conditions recorded.

Even a well-controlled change would remain a measurement result. It would not diagnose disease or prove that a product caused the change.

Sources 1, 5, 4

Deeper analysis

What the evidence means in practice

01

Each endpoint answers a different question

Surface pH describes hydrogen-ion activity at the measured surface. TEWL estimates outward water-vapour flux. Hydration instruments infer water-related properties of the stratum corneum through a device-specific physical signal. They may move together in some settings and diverge in others because they are not measuring the same thing.

This matters when a study uses one endpoint as shorthand for overall barrier health. A difference in pH does not automatically imply a difference in TEWL, and a hydration reading does not establish itch, comfort or disease severity. The Cobiella pilot illustrates this directly: group differences appeared for pH at two sites, while its TEWL and hydration methods did not distinguish the same groups.

Sources 4, 2

02

Biological signal and measurement noise can coexist

Shimada's controlled tape-stripping model showed TEWL increasing as the outer barrier was deliberately removed. That supports a biological connection between the endpoint and barrier disruption.

Lau-Gillard and Cobiella also show why an ordinary single TEWL reading needs caution. Repeat measurements can vary with device, investigator, site, day and dog. These findings are not contradictory: an endpoint can respond to a real biological change and still require careful standardisation to detect that change reliably.

For research, the stronger design repeats measurements under the same conditions, prespecifies how readings will be summarised and reports variability. For an owner, a lone number without this context should not become a diagnosis or buying rule.

Sources 6, 5, 4

03

Variation is part of the result, not an inconvenience

Oh mapped differences across 14 body sites in five Beagles. Schlake found age and regional effects in 77 varied dogs. Kwon found age- and breed-related differences in hydration and pH in 149 healthy dogs. These studies used different populations and methods, so their numbers should not be collapsed into one target.

Together they support a narrower and more useful conclusion: body site and population characteristics belong in the interpretation. A reference interval would need a clearly defined population, standardised instrument and protocol, and enough dogs to describe expected variation.

Sources 3, 1, 2

04

A shampoo number cannot complete the causal chain

Peña-Corona measured pH, viscosity and other characteristics of twenty commercial shampoos. This shows that finished products can differ in directly measurable ways. It does not show which product is mild, which dog will tolerate it or how skin measurements change after use.

To support a tolerance or barrier-response claim, evidence would need the marketed formula, intended dilution, contact time, rinsing, relevant canine population, prespecified outcomes and transparent adverse-event reporting. Product pH may be one recorded characteristic, but it is not a substitute for that evidence.

Source 7

Study-by-study data atlas

Canine skin pH is not one number

The charts below preserve each study’s population, endpoint and measurement unit. They do not combine unlike studies, manufacture a universal “normal” range or score a grooming product.

Download atlas CSVDownload atlas JSON
Median and observed range of skin pH by age group and body siteSix horizontal ranges from a study of 77 healthy dogs. Younger-than-12-week rows cluster around a median of 4.94. Older-than-12-week rows have medians from 6.12 to 6.22 and wider observed ranges. Counts are bilateral site measurements, not dogs.Age and measured siteSkin surface pH456789<12 weeks · Pinna4.94<12 weeks · Axilla4.94<12 weeks · Inguinal4.94>12 weeks · Pinna6.22>12 weeks · Axilla6.14>12 weeks · Inguinal6.12
Median (dot) and observed range (line) reported by Schlake et al. for intact skin. The ranges describe observations in this sample; they are not clinical reference intervals or product targets. Each n in the table is a count of bilateral site measurements, not a count of independent dogs.
Extracted skin pH observations from Schlake et al., Table 2
Age groupSiteMedian pHObserved minimumObserved maximumMeasurements
<12 weeksPinna4.944.345.7054
<12 weeksAxilla4.944.315.4354
<12 weeksInguinal4.943.975.3654
>12 weeksPinna6.224.938.1898
>12 weeksAxilla6.144.958.0697
>12 weeksInguinal6.124.408.1899

What this study contributes

77 healthy client-owned dogs from 24 breeds; 27 were younger than 12 weeks, and age data were available for 74 dogs. Measurements used one calibrated surface electrode at three bilateral sites. The observed age and site differences make a single universal target difficult to defend.

Limitation: Some measurements were unavailable because of dense hair, lack of cooperation or failure to obtain a stable reading. These observations are not clinical reference intervals.

Open the author manuscript →

Different endpoint · experimental model

Water-loss measurements respond to controlled barrier disruption

Ten healthy dogs: eight crossbreeds and two Beagles, aged 7–13 years. The study deliberately tape-stripped clipped skin. Its dose-response supports measurement sensitivity under those conditions, not a normal range, diagnostic threshold or shampoo effect.

Experimental TEWL after deliberate tape stripping, mean ± SD (g/m²/h)
Site0 strips5 strips10 strips15 strips20 strips
Lumbar20.59 ± 5.5128.17 ± 7.4744.87 ± 24.0266.61 ± 24.9487.58 ± 30.59
Inguinal20.17 ± 3.60Not reported33.37 ± 8.5363.94 ± 19.78129.05 ± 64.11
Open the full study →

Measurement conditions matter

Four studies add context without comparable chart data

2025 · full text

Variations in skin biophysical parameters with age, sex and breed in dogs

Hydration and pH differed across age groups, while sebum did not show a significant age-group difference.

Boundary: Measurements came from one inguinal site, so the study cannot establish anatomical-site differences.

View source record →

2010 · authoritative abstract

Mapping of the dog skin based on biophysical measurements

TEWL was highest at the footpad and head and lowest at the inguinal region.

Boundary: The sample was limited to five healthy male Beagles aged 2–4 years.

View source record →

2019 · authoritative abstract

Pilot study using five methods to evaluate skin barrier function in healthy dogs and in dogs with atopic dermatitis

The Skin-pH-Meter was the most repeatable device; the VapoMeter had the highest intra- and interobserver variability.

Boundary: The authors identify the work as a pilot study and call for optimisation and confirmation.

View source record →

2010 · authoritative abstract

Evaluation of a hand-held evaporimeter (VapoMeter) for the measurement of transepidermal water loss in healthy dogs

Mean coefficients of variation across repeated regional measurements were 20%–33%.

Boundary: The regional ranges came from only two individual dogs and are not coat-type reference ranges.

View source record →

Separate evidence unit

Product pH is not canine skin pH

20 commercial nonmedicated shampoos marketed in Mexico City and a surrounding suburban area; no dogs or skin were measured. The observed product range is useful descriptive context only. It does not establish a universal specification or predict an individual dog’s response.

Measured pH of 20 diluted commercial dog shampoosTwenty points range from pH 5.6 to 8.4. They are product measurements after a one-to-ten dilution and are not canine skin measurements.56789
Peña-Corona et al. measured 20 commercial shampoos after a 1:10 laboratory dilution. No dogs or skin were measured. This separate plot prevents product pH from being mistaken for canine skin pH or a compatibility score.
Extracted diluted product pH values from Peña-Corona et al.
Products1234567891011121314151617181920
Diluted pH5.66.06.87.17.07.87.97.07.57.17.07.67.07.27.68.18.28.28.38.4
Open the full study →

Evidence map

What each source adds—and where its answer stops

Each row keeps the useful finding beside its most important limit. This prevents a laboratory mechanism, database entry or regulation from quietly becoming a finished-product conclusion.

Evidence unit 01

Healthy-dog pH study

Source 1
Design or scope
Prospective; 77 client-owned dogs
What it contributes
Puppies younger than 12 weeks had lower readings than older dogs. Among dogs older than 12 weeks, inguinal pH differed by sex and pinna pH by hair colour; neither association appeared at every site.
Where the answer stops
Observed ranges do not establish one normal value, diagnosis or shampoo target.

Evidence unit 02

Hydration, pH and sebum variation

Source 2
Design or scope
Cross-sectional; 149 healthy dogs
What it contributes
Hydration and pH differed across age and breed groups, adding a larger and more recent population to the variation evidence.
Where the answer stops
Five reported breed groups and one study setting cannot represent every dog or establish clinical thresholds.

Evidence unit 03

Biophysical body-site map

Source 3
Design or scope
Five healthy male Beagles; 14 sites
What it contributes
Mapped TEWL, hydration and pH across multiple regions and showed that site matters.
Where the answer stops
Very small, homogeneous sample; useful for method questions, not universal reference values.

Evidence unit 04

Five-method repeatability pilot

Source 4
Design or scope
15 healthy and 15 atopic dogs; three investigators
What it contributes
The pH meter was most repeatable and the VapoMeter most variable. pH differed between groups at two sites, while TEWL and hydration did not.
Where the answer stops
Pilot sample and device-specific results do not make any endpoint diagnostic.

Evidence unit 05

VapoMeter variability study

Source 5
Design or scope
Healthy dogs; repeated TEWL measurements
What it contributes
Reported substantial repeated-measure variation and effects of site, day, individual dog and side-to-side differences.
Where the answer stops
Variability estimates apply to the studied protocol and do not invalidate TEWL under every controlled design.

Evidence unit 06

Experimental TEWL model

Source 6
Design or scope
Ten healthy dogs; tape stripping
What it contributes
TEWL rose as the stratum corneum was deliberately disrupted, supporting TEWL as a barrier-related endpoint under controlled conditions.
Where the answer stops
Experimental damage is not spontaneous disease and does not predict an individual product response.

Evidence unit 07

Commercial dog-shampoo measurements

Source 7
Design or scope
Twenty products marketed in Mexico City
What it contributes
Measured product pH ranged from 5.6 to 8.4 and viscosity also varied.
Where the answer stops
No canine tolerance or skin-response outcome was tested; product measurements are not skin measurements.

Transparent method

How this evidence map was assembled

Search recorded August 27, 2026. The source register contains 7 included evidence units and 1 separately labelled boundary source. We report retained sources directly; we do not claim a reproducible screening count where no public screening log exists.

Scope

Targeted PubMed discovery of canine biophysical-measurement studies plus veterinary guidance. Healthy and dermatology populations were included when the measurement method or interpretation was directly relevant. A 2025 study was added because it directly examined hydration and pH across age and breed groups.

Exclusion boundary

Treatment-only reports without reusable measurement information, non-canine records and sources that did not define the measured endpoint were excluded. The WSAVA document is retained only for the general care and veterinary-escalation boundary.

Recorded discovery routes

  1. 01PubMed: (dog OR canine) AND (skin pH OR transepidermal water loss OR hydration)
  2. 02PubMed: canine skin barrier AND (repeatability OR anatomical site OR measurement)
  3. 03PubMed: canine hydration pH age breed
  4. 04Official guidance: site:wsava.org dermatology skin coat care dog

Use the research

Questions that keep the conclusion proportionate

Questions for a reviewer

  • Which endpoint was measured, and what physical property does that instrument report?
  • At which anatomical site, under what temperature and humidity, and after what acclimatisation?
  • Were clipping, cleaning, anaesthesia, recent washing and topical products controlled?
  • Was the comparison repeated within the same dog and site, or made between different populations?
  • Are variability, uncertainty, missing observations and device limitations reported?
  • Does the conclusion stay within measurement interpretation rather than diagnosis or product suitability?

What stronger claims would need

  • A reference interval would need a broad, representative population measured with one standardised protocol and instrument.
  • A product-tolerance claim would need canine-appropriate evidence from the finished product under intended conditions of use.
  • A clinical claim would need a diagnostic or intervention design with an appropriate population, comparator and veterinary interpretation.

Limits

Limitations are part of the result

  • This was a targeted evidence map, not an exhaustive systematic review.
  • One organization screened and extracted records; no independent second reviewer repeated the work.
  • Full text was not available for every record, so numerical detail is limited to information that could be verified from accessible primary records.
  • No formal risk-of-bias tool or certainty-grading framework was applied.
  • No meta-analysis was appropriate because endpoints, populations, instruments and study purposes were heterogeneous.

Source register

Sources readers can inspect

  1. Source 01 · primary study record

    Schlake et al. Influence of physiological factors on skin pH in dogs

    Veterinary Dermatology. 2022;33(1):3-e2. Prospective study of 77 client-owned dogs.

  2. Source 02 · primary study record

    Kwon et al. Variations in skin biophysical parameters with age, sex and breed in dogs

    Veterinary Dermatology. 2025;36(5):689-695. Study of hydration, pH and sebum in 149 healthy dogs.

  3. Source 03 · primary study record

    Oh and Oh. Mapping of the dog skin based on biophysical measurements

    Veterinary Dermatology. 2010;21(4):367-372. Fourteen-site map in five healthy male Beagles.

  4. Source 04 · primary study record

    Cobiella et al. Pilot study of five canine skin-barrier methods

    Veterinary Dermatology. 2019;30(2):121-e34. Repeatability study in 15 healthy and 15 atopic dogs.

  5. Source 05 · primary study record

    Lau-Gillard et al. VapoMeter evaluation in healthy dogs

    Veterinary Dermatology. 2010;21(2):136-145. Evaluation of TEWL variability in healthy dogs.

  6. Source 06 · primary study record

    Shimada et al. TEWL reflects canine skin barrier function

    Journal of Veterinary Medical Science. 2008;70(8):841-843. Experimental tape-stripping model in ten healthy dogs.

  7. Source 07 · primary study record

    Peña-Corona et al. Measurements of commercial dog shampoos

    Polish Journal of Veterinary Sciences. 2022;25(2):213-221. Descriptive measurements of twenty products.

  8. Source 08 · official guidance · supplemental boundary

    Supplemental guidance: WSAVA Principles of Wellness - Dermatology

    General veterinary care and escalation guidance; not treated as a measurement-study record.