Table 1.

Characteristics of non-invasive diagnostic approaches.

Method	Current applications	Studying	Advantages	Disadvantages
Tape stripping	Non-invasive sampling of the upper epidermal layers (mainly stratum corneum)	Physiology of the stratum corneum	Non-invasive, no scarring, painless, repeatable, applicable at any anatomical location (e.g., face) and suitable for any age group (including children)	Depth of sampling varies between different skin conditions and different body sites
		Diagnostic markers	Provides valuable molecular information	Need storage access (freezer) and sample transport facility if not processed at site
		Treatment targets	Easy and quick to perform, no special training or professional knowledge is required
		Disease pathomechanism	Cost effective
		Disease monitoring	Potential as a non-invasive tool for diagnostic, disease activity and therapeutic response
		Epidermal wound healing
		Excretion of endogenous substances
		Percutaneous absorption of topical treatments—kinetics of drug delivery
		Treatment efficacy and toxicity (e.g., glucocorticoid therapy)
	Disruption of the skin barrier	Skin barrier function (TEWL)
	“Deep” tape stripping = Koebnerisation	Pathophysiology of psoriasis
Hair plucking	Research	Etiology and pathogenesis of diseases involving the hair follicle (LE, LPP, scarring vs. non-scarring alopecias)	Relatively non-invasive, repeatable, and suitable for any age group (including children)	Variability in the quality of hair follicle obtained
		Wound healing	Provides valuable molecular information	Restricted to patients with presence of “pluckable” hairs; so far only investigated for the scalp
		Therapeutic response	Easy and quick to perform, however, the examiner needs to be able to differentiate anagen from telogen hair	Need for further scientific data
			Potential as a non-invasive tool for diagnostic, disease activity and therapeutic response	Results may depend on hair cycle stage. The same hair cycle stage should be analyzed (e.g., anagen) depending on research question
				Need storage access (freezer) and sample transport facility if not processed at site
Trans-Epidermal Water Loss (TEWL)	Skin epidermal permeability/barrier function	Barrier defects in various pathologies (eczema, psoriasis)	Non-invasive, painless, repeatable, applicable at any anatomical location (e.g., face) and suitable for any age group (including children)	Lack of molecular information—lack of specificity as a diagnostic tool
		Treatment efficacy and toxicity (e.g., glucocorticoid therapy)	Validated measure, quick, and accurate	Need access to the instrument (Tewameter®) and specific software
				Application limited to epidermal pathologies
Skin elasticity	Skin elasticity measurements	Skin disorders characterized by stiffness (scleroderma, systemic sclerosis) and, other pathologies	Non-invasive, painless, repeatable, applicable at any anatomical location (e.g., face) and suitable for any age group (including children)	Lack of molecular information—lack of specificity as a diagnostic tool
		Skin aging		Variability (age, sun-exposure, anatomical location, ethnicity)
		Treatment efficacy and toxicity (e.g., glucocorticoid therapy)		Need access to the instrument (Cutometer®) and specific software