Skin is considered as the border defining the limits of the body from the external world and functions
as a barrier between the two. In this capacity, it has evolved to be an integral part of the innate and adaptive
immune system. Although many reviews have described skin inflammation and processes that lead to its
clinical manifestations, we are not aware of any reviews that have focused on immunologic activity occurring in
the absence of any visual inflammatory cues. In this review, we discuss the importance of subclinical
inflammation in human skin and its relevance to innate immune surveillance under physiologic conditions.
Reactive oxygen species generated by metabolic processes, ultraviolet radiation or oxidizers may damage
cells, initiating proinflammatory cascades. In addition to serving as structural skin components, keratinocytes
have significant immunologic activity: they secrete proinflammatory cytokines and mediators, including
interleukin (IL)-1α, IL-6, IL-10, tumor necrosis factor-α and granulocyte-macrophage colony-stimulating factor.
Infant skin is particularly susceptible to irritation, inflammation and infection, since skin barrier function is not
fully developed after birth and continues to mature throughout the first few years of life. Non-invasive methods
such as fluorescence spectroscopy, spectral imaging and diffuse reflectance spectroscopy, as well as
minimally invasive tape stripping, can be used to assess subclinical inflammatory markers in vivo, including
erythema, epidermal cell proliferation rate and cytokine concentrations. Appropriately formulated skin care
products may help maintain skin barrier integrity and enhance its capacity. In the future, assessment of
subclinical inflammation may help clinicians prevent acute or chronic inflammatory conditions of the skin.