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Scar tissues were collected from patients with keloids, hypertrophic scars and mature scars. Normal skin was obtained from healthy individuals. Clinical attributes were used to select which tissue to obtain but the distribution of the specific hyaluronan (HA) staining was then used for the definite classification of the various scar types. Light microscopic and ultrastructural analyses were performed with an HA-binding probe, antibodies for collagen I and III and staining for mast cells. Ultrastructural studies of keloids revealed an altered collagen structure in the dermal layers, with an abundance of collagen fibres of similar diameter in both the reticular dermis (RD) and the papillary dermis (PD) compared to normal skin. Furthermore, the keloids displayed epidermal changes, which involved the basement membrane (BM), with fewer hemidesmosomes and an altered shape of desmosomes in the entire enlarged spinous layer. The frequency of mast cells found in keloids was lower than in other scar tissues and normal skin. These alterations in epidermis could influence the hydrodynamic and cell regulatory properties of the wounded skin with impaired function and insufficient regulative capacity to hinder the ever-growing collagen tissue that is characteristic for keloids. (C) 2014 British Association of Plastic, Reconstructive and Aesthetic Surgeons. Published by Elsevier Ltd. All rights reserved.