The vermilion border is the normally sharp demarcation between the lip

Lip

Lips are a visible body part at the mouth of humans and many animals. Lips are soft, movable, and serve as the opening for food intake and in the articulation of sound and speech...

 (red colored) and the adjacent normal skin

Skin

-Dermis:The dermis is the layer of skin beneath the epidermis that consists of connective tissue and cushions the body from stress and strain. The dermis is tightly connected to the epidermis by a basement membrane. It also harbors many Mechanoreceptors that provide the sense of touch and heat...

. It represents the change in the epidermis from highly keratin

Keratin

Keratin refers to a family of fibrous structural proteins. Keratin is the key of structural material making up the outer layer of human skin. It is also the key structural component of hair and nails...

ized external skin to less keratinized internal skin. It has no sebaceous glands, sweat glands, or hair.

The vermilion border is important in dentistry

Dentistry

Dentistry is the branch of medicine that is involved in the study, diagnosis, prevention, and treatment of diseases, disorders and conditions of the oral cavity, maxillofacial area and the adjacent and associated structures and their impact on the human body. Dentistry is widely considered...

 and oral pathology as a marker to detect disease

Disease

A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

, such as in actinic cheilitis

Actinic cheilitis

Actinic cheilitis is a form of cheilitis which is the counterpart of actinic keratosis of the skin and can develop into squamous cell carcinoma. In actinic cheilitis, there is thickening whitish discoloration of the lip at the border of the lip and skin...

.

Vermilionectomy

A vermilionectomy (or sometimes vermillionectomy with two Ls) is the surgical removal of the vermilion border. It is sometimes performed to treat carcinoma

Carcinoma

Carcinoma is the medical term for the most common type of cancer occurring in humans. Put simply, a carcinoma is a cancer that begins in a tissue that lines the inner or outer surfaces of the body, and that generally arises from cells originating in the endodermal or ectodermal germ layer during...

of the lip.