Table 1.

Overview of studies measuring skin alterations during long-term spaceflight.

	N *	Mission Duration	Measures	Findings	Reference
Human data	1	340 days	Clinical case report	Post-flight erythema and skin sensitivity in gravity-dependent areas;	[12]
				Persistence of skin problems for 6 days;
				Successful treatment with nonsteroidal anti-inflammatory drugs, gabapentin, hydrotherapy, and massage.
	1	6 months	Hydration stratum corneum (Corneometer®), TEWL (Tewameter®), skin surface structure (SkinVisiometer®), skin elasticity (Cutometer®), skin ultrastructure (20-MHz ultrasound, DermaScan®)	Delayed epidermal proliferation	[16]
				coarser skin surface post-flight;
				Significant loss of elasticity of the cutis post-flight;
				Degradation of fiber structure in the cutis post-flight.
	2	long-term	Hydration stratum corneum (Corneometer ®), TEWL (Tewameter®), skin topography (VisioScan®), skin elasticity (Cutometer®), skin density (20 MHz ultrasound), skin morphology and metabolism (Multiphoton tomography MPTflex™).	Thinning of the epidermis post-flight	[17]
				decreased melanin concentration post-flight;
				Increased elastin/collagen ratio post-flight.
	6	>4 months	Hydration stratum corneum (Corneometer®),	Improvement in skin hydration and barrier function;	[18]
			TEWL (Tewameter®),	No apparent changes in skin surface;
			skin surface profile (VisioScan®),	Unchanged skin density, thickness and elasticity post-flight.
			skin elasticity (Cutometer®),
			skin density and thickness (20-MHz ultrasound, DermaScan®),
			capillary blood flow, flow velocity, hemoglobin concentration, hemoglobin oxygenation (O2C, LEA Medizintechnik GmbH).
Rodent data	3	3 months	Stained tissue sections for determining thickness of the dermis, hypodermis and panniculus carnosus, and number of growing hair follicles, hydroxyproline assay to determine skin collagen content and extractability, microarrays and RT-PCR.	Significant reduction in dermal thickness post-flight;	[20]
				Increased collagen turnover;
				Significant modulated ECM gene expression;
				Increased number of hair follicles in anagen phase accompanied by a high expression of specific hair follicles genes
				Modulation of transcripts encoding proteins related to striated muscle homeostasis.
	6	13 days	RT-PCR and microarrays, high-throughput metabolomics profiling, immunofluorescence staining for oxidative damage marker on skin tissue sections.	Alteration of expression of genes related to production and metabolism of ROS; Alteration of expression of genes related to production and metabolism of ROS;	[21]
				Altered expression of genes encoding MMPs involved in ECM remodeling.

* The number of test subjects or animals included in the study. ECM, extracellular matrix; MMPs, matrix metalloproteinases; ROS, reactive oxygen species; RT-PCR, reverse transcriptase-polymerase chain reaction; TEWL, transepidermal water loss (TEWL).