Anatomy refers to the science of the structure of living organisms and physiology refers to the science associated with their functions. It’s easy to take the eyelashes for granted. They sit over our eyes like a hairy little roof and typically don’t require much attention. But there’s a lot going on behind the scenes. Here we look at eyelash anatomy, purpose, and evolution. The anatomical term for eyebrows is supercilia (singular: supercilium) from Latin. Supercilia also refer to plumage around the eyes of certain birds!

A few different muscles are responsible for the many expressions human beings make with our eyebrows. The corrugator supercilii muscle is located on the side of the eyebrow closest to the nose. There is one over each eye. They pull the eyebrows downward and towards the middle of the face. This movement is part of frowning and is also a response to intense light (squinting). Repeated use of this muscle over time can result in vertical wrinkles on the forehead above the nose. 

Next to the corrugator supercilii muscles and a little farther away from the nose are the depressor supercilii muscles. The depressor supercilii muscles also contribute to the downward turn of the brows near the nose, causing frowning and squinting. The procerus is one muscle positioned between the eyes and along the upper bridge of the nose. When contracted, the procerus pulls down the inner corners of the eyebrows (closest to the nose), resulting in a frown. 

The orbicularis oculi are a larger muscle that surrounds the eye and has a few purposes. The part of the orbicularis oculi muscle towards the nose assists with frowning. The part of the orbicularis oculi muscle near the outer (“tail”) end of the brow is a lateral brow depressor. This means that this section of the muscle pulls the brows down a bit and counterbalances the action of the frontalis muscles, which pull the eyebrows up. The occipitofrontalis (“frontalis”) muscles are arranged vertically under our forehead, one above each eyebrow. These muscles allow us to raise our brows by drawing back our forehead. In humans, the only function of these muscles is to show facial expressions, such as raising the eyebrows to indicate surprise. Over the years, using this pair of muscles can create horizontal expression lines (wrinkles) in the mid-forehead.

90% of human hair is made up of a protein called keratin along with a pigment called melanin that provides the color. The other 10% is water that keeps it hydrated. Keratin is a hard-wearing fibrous protein, and its strands are compacted and chemically held together by strong disulphide bonds and hydrogen bonds. As with head hair, eyelashes grow from follicles along the eyelid. Follicles are in the dermis, the layer beneath the uppermost skin layer called the epidermis. The papilla is a large structure at the base of the hair follicle where the growth takes place. The bulb comprises of growing cells that divide in its lower part and then pushes up. Melanocyte cells make the melanin pigment there. When the cells harden and reach the upper part, they arrange themselves into cylindrical layers. The outermost part of the hair is the cuticle. It is formed from dead cells that overlap into layers to form scales. These give the hair strength and provides a hard surface to protect the cortex. The cortex is the middle layer. It’s the main bulk of the hair comprising of keratin fibers and melanin. The inner most part is the medulla that contain cells. It’s not usually present s in finer hair.

Eyebrow hair growth happens in a cycle of stages. There’s the anagen stage, when hair is actively growing; the catagen stage, when hair is transitioning from growth to rest, and the telogen stage, when hair is resting or shedding. Some experts include a fourth stage, the exogen stage, which is characterized specifically by shedding. After an eyebrow hair goes through all stages in the cycle, the process begins again.

  • For eyebrows the anagen (growth) stage lasts between 4 to 7 months. (Compare this to the 2 to 7+ years for scalp hair!)
  • For eyebrows, the catagen (transitional) stage usually lasts for 3 to 4 weeks.
  • The telogen (rest/shedding) stage lasts for about 2 to 4 months for scalp hair, but for eyebrows, the telogen phase is a lot longer: 9 months.

The physical reason we have eyebrows is to keep sweat, water, and debris out of eyes. Eyebrows form a web of hair that can catch dirt, dust, and dandruff before it falls into the eyes. Brows are also slanted on the side, causing liquid to flow away from the eyes. In many people eyebrows, along with the slight brow ridge in humans, help shade the eyes from the bright light.

Another possible purpose for brows is to trigger physical sensations that help us detect small foreign objects, such as insects or plant particles, that threaten to get into our eyes.

Expressing emotions through eyebrow movements is part of being human. In fact, it’s even more basic than that. It’s part of being a primate, as all primates send social messages through eyebrow activity. But unlike many of our primate cousins, humans have a high level of contrast between our brows and hairless skin that circles them, thus emphasizing the brow region during communication.

Eyebrows’ importance is also passed on through culture. For centuries, in cultures worldwide, abundant hair has been linked to fertility, strength, and power. This association has often extended to eyebrows. Ancient people beautified their brows with makeup and shaping, and people do now. 

Eyebrows can display facial symmetry. And they can be altered cosmetically to disguise asymmetry. Facial symmetry is often mentioned as a key factor in human attractiveness. People may be programmed to associate symmetrical features with health of potential mates.

Ancestors of modern humans had a distinct bony brow ridge, a feature which is thought to have restricted their eyebrow movements. The purpose of the brow ridge isn’t entirely clear, but modern humans no longer have it. Did the loss of the brow ridge enable homosapiens to better communicate and collaborate non verbally? Collaboration is key for the survival and advancement of a highly social species. Right now, this idea is still a theory.

Another interesting theory about how we got our eyebrows is suggested by Joseph Jordania, who believes that sleeping early humans’ upward arching eyebrows, along with our downward arching eyelashes, created oval eye spots on our face. These eye spots made it look as if our eyes were open when we were sleeping, thus fending off stealth predators, such as large cats, that don’t like to be noticed as they’re sneaking up on their prey.

Inflammation is part of the complex biological response of vascular tissues to harmful stimuli, such as pathogens, damaged cells, or irritants. Inflammation is a protective attempt by the body to remove the injurious stimuli and to initiate the healing process. When tissue cells become injured, they release several chemicals that initiate the inflammatory response. Inflammation is characterized by 5 distinct signs, each of which is due to a physiological response to tissue injury. 

The area becomes painful (dolar), swelling occurs (tumor), vasodilation causes redness (rubor) and temperature increase within the tissues (calor) as pain and swelling intensify impairment of function occurs (functio laesa). It is important to understand how the skin reacts to inflammation following the superficial wounding caused by micro-pigmentation.

With this understanding you will be able to advise your clients on aftercare during the expected downtime period following micropigmentation treatment.

Acute inflammation is a short-term process, usually appearing within a few minutes of the cell trauma being induced by micro-pigmentation. Damage occurs from the initial trauma to the cells and tissues, where the local network of ruptured blood vessels bleeds into the tissue spaces and the cell walls rupture. Cellular damage occurs leaving dead and dying cells disrupted by the trauma. Within seconds and up to 10 minutes after the initial trauma local blood vessel constriction occurs. This vasoconstriction minimizes blood loss from the area and initiates clotting (hematoma). However, the resulting hypoxia causes tissue necrosis at the primary injury site. This triggers the lysosomes (waste disposal unit within a cell) found within the dead and damaged cells to start to leak digestive enzymes through their ruptured membranes. These enzymes act as inflammatory mediators causing surrounding arterioles and capillaries to dilate (calor and rubor) and cause stimulation of surrounding pain receptors (dolar).

Pain receptors are specialized nerve endings located throughout the body in most body tissues. Once the nerve endings are stimulated by these chemicals, they begin firing the nerves that are connected to them and send pain signals to the spinal cord and brain. As blood vessels dilate, they become more permeable and within a few hours’ exudation increases. As the vessel walls enlarge the speed of flow decreases due to vessels being packed with cells. The stasis of blood allows leukocytes to move along the endothelium and escape through the capillary wall, along with plasma and other circulating defensive substances such as antibodies, phagocytes, and fibrinogen to the site of the injury. The arrival of these specialized cells (antibodies, phagocytes) lead to the engulfing of dead cells, foreign material, or infectious agents.

 As fluid moves out of the capillaries, stagnation of flow and clotting of blood in the small capillaries occurs at the site of injury. This process is caused as fibrinogen produces fibrin which forms a mesh of fibers creating a collection site for red blood cells (hematoma) and traps micro-organisms preventing their movement further from the injury site. This increased collection of fluid into the tissue spaces causes it to swell (tumor). This expansion of chemical activity in surrounding tissues produces the zone of secondary injury. 

Normally, lymphatic vessels drain the area of excess fluid and cells. However following trauma within the tissues, the lymph vessels become blocked. The excess fluid and cells collect in the spaces between the tissues around the site of the trauma and oedema occurs. As fluid and cells try to occupy a limited amount of space, the pressure caused on nerve endings is perceived as pain. Many lymphatic channels lie directly beneath the skin. Oedema which is the swelling or natural splinting process of the body has 2 basic components. The first is a liquid, which can be evacuated by the circulatory system and the second is comprised of proteins which must be evacuated by the lymphatic system. The lymph vessel diameter and the flow of the lymph system being decreased causes the swelling to occur in the first 24 hours following micro-pigmentation. Within 12 hours of injury macrophages move in to digest tissue debris to clear the way for peripheral cells to begin the process of mitosis. 

Fibrocytes also move into the area to start the process of fibroplasia. Tissue repair overlaps the inflammatory process and within 48 to 72 hours the hematoma is sufficiently diminished to allow for this new growth of tissue. As the damaged skin within the epidermal layers begins to regenerate, the deeper soft tissues will replace damaged cells with scar tissue. The fibroblasts release collagen, elastin and reticulin fibers forming a mesh network to reconnect tissues. Over the next 3 day’s mitosis continues and all around the injured area capillary loops develop (angiogenesis). These sprouting vessels originate from pre-existing vessels and appear as minute red granules, hence the name granulation tissue. As the circulation is increased by these additional blood vessels replacing damaged ones, more oxygen and nutrients become readily available to these cells to aid in speeding up the healing process. When circulation is increased it automatically increases lymphatic flow with the movement of tissue fluid between the 2 systems, allowing the excess build-up of lymph to be drained reducing swelling.

Inflammation is the important first stage of healing damaged tissue. Healing cannot occur until inflammation has come and gone. Therefore, we cannot prevent inflammation, however we can speed up the processes involved by application of cold therapies following micro-pigmentation for the first 72 hours following treatment.

Whenever trauma occurs to the surface of the epidermis the protective barrier will be impaired, the application of micro-pigmentation treatment will cause a burn, cut or puncture wound to the area infused with pigment. The epidermis will protect this impairment by the formation of a scab, the size and extent of this scab will be in relation to the trauma caused (scab in picture is not caused by PMU treatment).x the scab may be minute and clearer in color if only lymph vessels has been disturbed, however if capillary damage was involved there will be droplets of blood also in the scab formation. When treating more mature clients or clients with more sensitive skin, there is a higher tendency to bruise and tear the skin resulting in a greater inflammatory response. This will result in a slightly longer healing process.

The healing process can differ from one client to another; there are several factors to consider such as:

  • Age
  • Health of client
  • Client lifestyle

As a rule, the older you are (once passed 25 years) the slower the expected healing rate. Remember the superficial tissues will display signs of healed skin long before the internal layers have completed the full healing process. The following is a general guideline to expected healing rates:

Brows: Age 0-40, 4 weeks | Age 40-60, 4 weeks | Age 60+, 6 weeks