Skin Color

Major Pigments Contributing to Skin Color

The color of human skin is determined by the presence and concentration of three primary pigments. These pigments not only influence appearance but also play roles in protection and physiological function.

• Melanin: A pigment produced by melanocytes, found in the epidermis. It can be yellow, reddish brown, or black. Melanin protects against ultraviolet (UV) radiation by absorbing harmful rays.

• Carotene: An orange-yellow pigment, also found in certain vegetables (e.g., carrots). Carotene accumulates in the stratum corneum and fatty tissue of the skin.

• Hemoglobin: The red coloring from blood cells in dermal capillaries. The oxygen content of hemoglobin determines the extent of red coloration in the skin.

Example: Individuals with higher melanin levels tend to have darker skin, which provides greater protection against UV damage.

Clinical Variations in Skin Color

Changes in skin color can indicate underlying physiological or pathological conditions.

• Redness (Erythema): Caused by embarrassment, inflammation, hypertension, fever, or allergy.

• Pallor (Blanching): Due to emotional stress, anemia, low blood pressure, or impaired blood flow.

• Jaundice: A yellow cast indicating liver disorder due to accumulation of bilirubin.

• Bruises (Hematomas): Black and blue marks resulting from blood escaping from vessels and clotting beneath the skin.

Example: Jaundice is commonly seen in newborns and patients with liver disease.

Appendages of the Skin

Overview of Cutaneous Glands

The skin contains several types of appendages, including glands and hair follicles, which serve protective and regulatory functions.

• Sebaceous (Oil) Glands

• Sudoriferous (Sweat) Glands

• Hair and Hair Follicles

• Nails

Additional info: All cutaneous glands are classified as exocrine glands, meaning they secrete their products through ducts to the skin surface.

Sebaceous (Oil) Glands

Sebaceous glands are found throughout the skin except on the palms and soles. They secrete sebum, an oily substance that maintains skin and hair health.

• Functions of Sebum:

  • Makes skin soft and moist

  • Prevents hair from becoming brittle

  • Kills bacteria (antimicrobial properties)

• Most sebaceous glands empty into hair follicles; some open directly onto the skin surface.

• Glands are activated at puberty due to increased androgen levels.

Example: Overactivity of sebaceous glands can lead to acne formation.

Sudoriferous (Sweat) Glands

Sudoriferous glands are widely distributed in the skin and are essential for thermoregulation and excretion.

• Produce sweat, which is composed of water, salts, vitamin C, and metabolic wastes.

• Two main types:

  • Eccrine glands

  • Apocrine glands

Eccrine Glands

Eccrine glands are more numerous and found all over the body. They open via ducts to sweat pores on the skin's surface.

• Produce acidic sweat (pH 4-6)

• Composition: Water, salts, vitamin C, traces of metabolic waste

• Primary function: Body temperature regulation through evaporative cooling

Example: Sweating during exercise helps prevent overheating.

Apocrine Glands

Apocrine glands are located mainly in the armpit and genital areas. Their ducts empty into hair follicles.

• Begin functioning at puberty

• Secrete sweat containing fatty acids and proteins, resulting in a milky or yellowish color

• Play a minimal role in temperature regulation

Additional info: Apocrine sweat can be broken down by bacteria, leading to body odor.

Structure of the Skin

The skin is composed of three main layers: epidermis, dermis, and hypodermis. Each layer contains specialized structures and cells.

• Epidermis: Outermost layer, contains keratinocytes and melanocytes.

• Dermis: Middle layer, contains connective tissue, blood vessels, nerves, and appendages.

• Hypodermis (Subcutaneous layer): Deepest layer, composed mainly of adipose tissue.

Example: The dermis houses sweat glands, sebaceous glands, hair follicles, and sensory receptors.

Hair and Hair Follicles

Hair is produced by hair follicles and serves protective and sensory functions.

• Found body-wide except for palms, soles, nipples, and lips

• Produced by hair follicle; root is enclosed in the follicle, shaft projects from the skin surface

• Consists of hard, keratinized epithelial cells

• Melanocytes provide pigment for hair color

• Hair grows in the matrix of the hair bulb in the stratum basale

Additional info: Hair growth is influenced by genetics, hormones, and nutrition.

Hair Anatomy

• Central Medulla: Innermost layer

• Cortex: Surrounds the medulla

• Cuticle: Outermost layer, most heavily keratinized

• Melanin provides color

Associated Hair Structures

• Hair Follicle: Composed of an inner epithelial root sheath and outer fibrous sheath

• Dermal Region: Provides blood supply to the hair bulb

• Arrector Pili Muscle: Connects to the hair follicle and pulls hairs upright when cold or frightened

Nails

Nails are heavily keratinized, scalelike modifications of the epidermis that protect the distal phalanges.

• Stratum basale extends beneath the nail bed and is responsible for nail growth

• Lack of pigment makes nails colorless

Parts of a Nail

• Free Edge: The part that extends beyond the finger or toe

• Body: The visible attached portion

• Nail Folds: Skin folds that overlap the edges of the nail; the cuticle is the proximal edge

• Root: Embedded in skin

• Nail Matrix: Responsible for nail growth