Skin

The Science of the Integumentary System

Your body's largest organ — a living, multilayered system that protects, regulates, and senses. Understanding its structure is the foundation of every effective formulation.

1.5–2m²

Surface Area

3–4mm

Average Depth

30 days

Full Cell Renewal

16%

of Body Weight

Overview

What is the skin?

The skin is the body's largest organ, made of water, protein, fats and minerals. It protects your body from germs and regulates body temperature. Nerves in the skin help you feel sensations like hot and cold.

Your skin, along with your hair, nails, oil glands and sweat glands, is part of the integumentary system — the body's outer covering. Understanding its architecture informs how active ingredients penetrate, interact, and deliver results.

What are the layers of the skin?

Three layers of tissue make up the skin:

  • Epidermis, the top layer.
  • Dermis, the middle layer.
  • Hypodermis, the bottom or fatty
    layer.

What does the epidermis (top layer of skin) do?

Your epidermis is the top layer of the skin that you can see and touch. Keratin, a protein inside skin cells, makes up the skin cells and, along with other proteins, sticks together to form this layer.

  • Acts as a protective barrier: The epidermis keeps bacteria and germs from entering your body and bloodstream and causing infections. It also protects against rain, sun and other elements.
  • Makes new skin: The epidermis continually makes new skin cells. These new cells replace the approximately 40,000 old skin cells that your body sheds every day. You have new skin every 30 days.
  • Protects your body: Langerhans cells in the epidermis are part of the body’s immune system. They help fight off germs and infections.
  • Provides skin color: The epidermis contains melanin, the pigment that gives skin its color. The amount of melanin you have determines the color of your skin, hair and eyes. People who make more melanin have darker skin and may tan more quickly.

What does the dermis (middle layer ofskin) do?

The dermis makes up 90% of skin’s thickness. This middle layer of skin:

  • Has collagen and elastin: Collagen is a protein that makes skin cells strong and resilient. Another protein found in the dermis, elastin, keeps skin flexible. It also helps stretched skin regain its shape.
  • Grows hair: The roots of hair follicles attach to the dermis.
  • Keeps you in touch: Nerves in the dermis tell you when something is too hot to touch, itchy or super soft. These nerve receptors also help you feel pain.
  • Makes oil: Oil glands in the dermis help keep the skin soft and smooth. Oil also prevents your skin from absorbing too much water when you swim or get caught in a rainstorm.
  • Produces sweat: Sweat glands in the dermis release sweat through skin pores. Sweat helps regulate your body temperature.
  • Supplies blood: Blood vessels in the dermis provide nutrients to the epidermis, keeping the skin layers healthy.

What does the hypodermis (bottom layerof skin) do?

The bottom layer of skin, or hypodermis, is the fatty layer. The hypodermis:

  • Cushions muscles and bones: Fat in the hypodermis protects muscles and bones from injuries when you fall or are in an accident.
  • Has connective tissue: This tissue connects layers of skin to muscles and bones.
  • Helps the nerves and blood vessels: Nerves and blood vessels in the dermis (middle layer) get larger in the hypodermis. These nerves and blood vessels branch out to connect the hypodermis to the rest of the body.
  • Regulates body temperature: Fat in the hypodermis keeps you from getting too cold or hot.

What else makes up the skin?

One inch of your skin has approximately 19 million skin cells and 60,000 melanocytes (cells that make melanin or skin pigment). It also contains 1,000 nerve endings and 20 blood vessels

The Science of Hair Growth

Hair Follicle

Hair follicles are structures within your skin that grow your hair. You’re born with millions of hair follicles in your skin. You can’t pull out hair follicles. Damaged hair follicles lead to hair loss or reduced hair growth.

Overview

What is a hair follicle?

A hair follicle is a tube-like structure (pore) that surrounds the root and shaft of a hair. Hair follicles exist in the top two layers of your skin. You’re born with over 5 million hair follicles in your body and over one million hair follicles on your head. As you age, hair grows out of your hair follicles.

Your hair follicle is one of a few structures in your body that can stop functioning and begin functioning again (degenerate and regenerate). This process helps with hair growth on your body.

5M+

Follicles on the body

1M+

Follicles on the head

1 cm

Growth per month

2–7 yr

Active growth phase

Function

What is the function of a hair follicle?

The function of a hair follicle is to grow your hair. In addition to promoting hair growth, your hair follicles do the following jobs:

  • Help repair your skin after a wound or an injury.
  • Form new blood vessels  (angiogenesis).
  • Form new nervous system neuron cells (neurogenesis).

How does a hair follicle help with wound
healing?

The cells in your hair follicles help your body heal after a wound. When your body receives an injury, the cells within your hair follicles are closest to the wound and quickly move to the site of the wound to start the healing process. Your hair follicle cells assist your body’s white blood cells in your immune system.

How does hair grow out of a hair follicle?

Hair grows in cycles within your hair follicle:

Anagen: Growth Phase

The first phase of hair growth takes between two to seven years. Growth begins at the root (dermal papilla) in your hair follicle, which gives your hair blood supply and the nutrients it needs to grow. Your hair grows about 1 centimeter per month.

Catagen: Transition Phase

The second phase of hair growth occurs when the hair transitions from a growing phase to a resting phase, which takes about two weeks. During this phase, your hair detaches from your blood supply.

Telogen: Shedding Phase

The final phase of hair growth is the inactive phase, where your hair sheds or falls out of your hair follicle. This phase takes up to four months.

Where are hair follicles located?

Wherever you have hair on your body, you also have hair follicles. Hair follicles originate in the first and second layers of your skin (epidermis and dermis). Follicles holding your terminal hair, or the hair that grows on your scalp, eyelashes and eyebrows, extend into the first and second layer of your skin and sometimes into the third layer (subcutaneous tissue).

What does a hair follicle look like?

A hair follicle looks like a long tube that holds your hair. It's in the shape of a cylinder with a rounded bottom in your skin. The top of the cylinder is an open hole, which is where your hair grows out. Your follicle is similar to a sock; your hair is your foot that goes into your sock.