Do you know what elastin is? How about the difference between the dermis and the epidermis? Skin has a vocabulary of its own. Knowing some of the terms can help you understand your aging skin.

Age spots: Brown spots found on the skin that are visible evidence of accumulated long-term sun damage, known to dermatologists as "lentigines." Also called "liver spots".

Collagen: A fibrous protein found in the connective tissue that causes skin to be plump.

Dermatologist: Physician who specializes in diagnosing and treating diseases and disorders of the skin, hair, nails and mucous membranes.

Dermis: The layer of the skin beneath the epidermis. The dermis is largely fibrous and contains collagen and elastin—the proteins responsible for the support and elasticity of the skin. The dermis also contains tiny sensory nerve endings and blood vessels.

Elastin: A protein similar to collagen that is the principal structural component of resilient fibers, which enable skin to snap back when stretched.

Epidermis: Uppermost layer of the skin. The epidermis is highly cellular and divided into layers: the basal (bottom) layer that produces new cells and contains melanocytes or pigment-producing cells; a thick prickle cell layer; the granular cell layer and the stratum corneum or top layer.

Esthetician: A qualified skin care specialist trained to administer beauty treatments for the skin.

Melanin: A brown pigment produced by pigment producing skin cells (melanocytes). Increased amount of melanin pigment results in a tanned hue following exposure to ultraviolet light.

Photodamage: Skin damage and deterioration—fine wrinkling, brown patches and roughness—caused by long-term effects of everyday exposure to the sun's harmful ultraviolet rays.

Pigment: The coloring matter found in the skin.

Retinoic Acid: Vitamin A acid typically used in products for the treatment of acne and certain signs of photodamage.

Stratum Corneum: Outermost layer of dead cells in the epidermis that protects living tissue from external stimuli and forms a barrier to keep moisture in.

Sun Damage: See photodamage.

Tretinoin: A synthetic form of vitamin A, like the one naturally occurring in your body; the active ingredient in RENOVA.

Ultraviolet A (UVA), Ultraviolet B (UVB): Two types of solar radiation within the ultraviolet range that reach the earth's surface, resulting in photodamage, suntan, sunburn and, potentially, skin cancer.