Thick skin refers to skin that contains all five of the major layers of the epidermis. It is only found on the soles of the feet, the palms of the hand and the fingertips, all areas which typically experience a lot of abrasion. The rest of the skin on the human body is classified as thin skin and only contains four of the five layers of the epidermis.
The layers of the epidermis include the stratum basale, which is a single layer of cells immediately above the dermis; the stratum spinosum, which supports the skin; the stratum granulosum, which produces keratin; the stratum lucidum, which protects against harmful ultraviolet rays; and the stratum corneum, which contains dead cells filled with keratin to protect the cells underneath it from drying out.
The fourth layer of the epidermis, the stratum lucidum, is only found in thick skin. It has no sebaceous glands or hair follicles. It does, however, contain sweat glands. The dermis layer under thick skin tends to be thinner than that underlying typical thin skin; as a result, thin skin is easier to suture than thick skin. Some of the areas of thin skin on the body, such as the skin covering the eyelids, only contain three of the layers of the epidermis.