A unibrow is part of normal human variation, but can also stem from developmental disorders. A unibrow is a recognized feature of Cornelia De Lange syndrome, a genetic disorder whose main features include moderate to severe learning difficulties, limb abnormalities such as oligodactyly (fewer than normal fingers or toes) and phocomelia (malformed limbs), and facial abnormalities including a long philtrum (the slight depression/line between the nose and mouth).

Other medical conditions associated with a unibrow include:

- Waardenburg Syndrome;

- Patau Syndrome;

- Smith-Lemli-Opitz Syndrome;

- Sanfilippo Syndrome;

- 3p Deletion Syndrome;

- Chromosome Deletion Dillan 4p Syndrome (Wolf–Hirschhorn Syndrome);

- Gorlin Syndrome (Basal Cell Nevus Syndrome);

- Frontometaphyseal Dysplasia;

- ATRX Syndrome;

- Chromosome 9q34 Microdeletion Syndrome or Kleefstra syndrome.

There are various causes of madarosis.

- Ophthalmological conditions: blepharitis is an infection of the eyelid. Anterior blepharitis is either "staphylococcal blepharitis,"or "seborrhoeic blepharitis" and posterior blepharitis is due to the meibomian gland.

- Dermatologic conditions: there are multiple types of dermatological conditions that can result in madarosis. These include Atopic dermatitis, Seborrhoeic dermatitis atopic dermatitis, and Psoriasis on the eyelids can result in madarosis. Others include: frontal fibrosing alopecia, ulerythema ophryogenes, acne rosacea, telogen effluvium, follicular mucinosis, and cutaneous sarcoidosis.

- Nutritional defects: Severe malnutrition can cause chronic hair loss. Hypoproteinemia causes hair loss by early onset of telogen. Zinc deficiencies like acrodermatitis enteropathica, can lead to the loss of eyebrow/eyelash hair. Other deficiencies like biotin and iron make it possible for loss of hair as well.

- Infections: There are many bodily infections that can cause the loss of eyelashes/eyebrows. The most common infection may be leprosy, such as lepromatous leprosy. Syphilis or other viral infections like herpes or HIV can cause the loss of eye hair as well. Fungal infections, like paracoccidioidomycosis, trichophyton, or microsporum, are also possible infection causes.

- Trauma: Most trauma injuries cause madarosis from the psychological standpoint, known as trichotillomania

- Drugs/Medications: Crack cocaine or chemotherapy drugs. Other drugs include:propranolol, valproic acid, barbiturates, MMR vaccine, botulinum toxin, epinephrine, antithyroid drugs, anticoagulants, and lipid-lowering drugs

- Genetics

- Autoimmune disorders: alopecia areata, discoid lupus erythematosus, chronic cutaneous lupus erythmatosus, Graham-Little syndrome, and Parry Romberg syndrome

- Other diseases: hypothyroidism, hyperthyroidism, hypoparathyroidism, hypopituitarism, and amyloidosis

There only prevention method is determining the underlying condition before treatment options are too late.

Other causes of hair loss include:

- Alopecia mucinosa

- Biotinidase deficiency

- Chronic inflammation

- Diabetes

- Lupus erythematosus

- Pseudopelade of Brocq

- Telogen effluvium

- Tufted folliculitis

Among most Westerners, the region between the eyebrows is often plucked, waxed, shaved, or treated with electrology or laser hair removal.

Research is looking into connections between hair loss and other health issues. While there has been speculation about a connection between early-onset male pattern hair loss and heart disease, a review of articles from 1954 to 1999 found no conclusive connection between baldness and coronary artery disease. The dermatologists who conducted the review suggested further study was needed.

Environmental factors are under review. A 2007 study indicated that smoking may be a factor associated with age-related hair loss among Asian men. The study controlled for age and family history, and found statistically significant positive associations between moderate or severe male pattern hairloss and smoking status.

Vertex baldness is associated with an increased risk of coronary heart disease (CHD) and the relationship depends upon the severity of baldness, while frontal baldness is not. Thus, vertex baldness might be a marker of CHD and is more closely associated with atherosclerosis than frontal baldness.

There are two major pathways. In the non-scarring pathway, the hair follicles remain intact which could potentially be reversed with the proper diagnosis and treatments. In the Scaring pathway, the follicles are permanently lost due to tissue damage, autrophy, or inflammation.

The severity of the pre-existing condition determines which type of madarosis occurs.

- Ophthalmologic conditions: there are multiple types of infections and are common. The gray line of the eye is a line that divides the eyelid into parts: anterior part is skin and muscle while posterior is tarsus and conjunctiva. The blepharitis is classified based on the type of eyelid involvement. Anterior blepharitis is either "staphylococcal blepharitis,"or "seborrhoeic blepharitis" which have symptoms of the presence of scales that are along the hair shaft. Posterior blepharitis is usually due to meibomian gland dysfunction.

- Dermatologic conditions: there are multiple types of dermatological conditions that can result in madarosis dependent on the location. Atopic dermatitis is associated with allergic disorders and affects the lower eyelid. Seborrhoeic dermatitis can be seen as the scaling of the eyebrows. Loss of eyebrows is commonly seen from both atopic and seborrhoeic dermatitis due to continuous scratching/touching. Psoriasis on the eyelids can result in madarosis. Others include: frontal fibrosing alopecia, ulerythema ophryogenes, acne rosacea, telogen effluvium, follicular mucinosis, and cutaneous sarcoidosis.

- Nutritional Defects: Zinc is important in hair growth and the lack of zinc can cause hair loss, specifically madarosis.The main proteins in hair are biotin and iron so deficiencies would result in a loss of hair.

- Infections: Unilateral madarosis (only one eye) may occur in tuberculoid leprosy from granulomatous infiltration of hair follicles ultimately destroying them. Infections like syphilis by causing a moth-eaten appearance of the eyebrow hair loss. Viral infections like herpes or HIV can cause scarring of the eyelid, causing loss of hair. Various fungal infections like paracoccidioidomycosis can cause lesions and changes in the hair locations of the eyelid.

- Trauma: Trichotillomania is a psychological disorder where the hair is pulled out or breakage occurs when anxious. Both trichoteiromania (hair loss from constant rubbing) and trichotemnomania (hair loss from constant shaving of the hair) can result in hair loss.

- Drugs/Medications: The heart medication amiodarone has been reported to commonly cause loss of eyelashes and eyebrows. Cocaine abuse has shown hair loss due to the hot vapors traveling up causing burning of the hair of the eyebrows or eyelashes. Radiotherapy and chemotherapy can cause hair loss due to the eradication of the hair cells, especially when used to treat ocular tumors.

- Genetics: Some of the diseases listed in the causes can be inherited.

Frontal Fibrosing Alopecia has been most often reported in post-menopausal women with higher levels of affluence and a negative smoking history. Autoimmune disease is found in 30% of patients.

If the condition thickens, turns red and irritated, starts spreading, appears on other body parts, or if the baby develops thrush (fungal mouth infection), fungal ear infection (an ear infection that does not respond to antibiotics) or a persistent diaper rash, medical intervention is recommended.

Severe cases of cradle cap, especially with cracked or bleeding skin, can provide a place for bacteria to grow. If the cradle cap is caused by a fungal infection which has worsened significantly over days or weeks to allow bacterial growth (impetigo, most commonly), a combination treatment of antibiotics and antifungals may be necessary. Since it is difficult for a layperson to distinguish the difference between sebaceous gland cradle cap, fungal cradle cap, or either of these combined with a bacterial infection, medical advice should be sought if the condition appears to worsen.

Cradle cap is occasionally linked to immune disorders. If the baby is not thriving and has other problems (e.g. diarrhea), a doctor should be consulted.

Although the pathogenesis of Frontal Fibrosing Alopecia is poorly understood, autoimmune reaction and hormonal factors may play a role.

Assurances that this condition will clear as the baby matures are very common. However, studies have shown that the condition occasionally persists into the toddler years, and less commonly into later childhood. It tends to recur in adolescence and persists into adulthood. In an Australian study, about 15 percent of previously diagnosed children still had eczema 10 years later. Sometimes, cradle cap turns into atopic dermatitis. Rarely, it turns out to be misdiagnosed psoriasis.

Respiratory complications are often cause of death in early infancy.

This disease is often found during the first two months of an infants life, breast-fed infants with a higher chance. Male and female infants are affected equally.

The cause of this disease is unknown; some infants may have a severe case, others may have immunodeficiency.

The first gene that could cause the syndrome is described recently and is called NF1X (chromosome 19: 19p13.1).

The Sign of Hertoghe or Queen Anne's sign is a thinning or loss of the outer third of the eyebrows, and is a classical sign of hypothyroidism or dermatitis atopica, but it can also be detected in lepromatous leprosy. The sign is named after Eugene Hertoghe of Antwerp, a pioneer in thyroid function research.

The association with Anne of Denmark is based on portraiture, although history does not suggest that she suffered an underactive thyroid. The eponym is disputed by some, though it has been suggested that Anne of France, Anne of Brittany, Anne of Austria, Anne Boleyn and Anne of Cleves may all be eliminated as candidates.

Alopecia universalis can occur at any age, and is currently believed to be an autoimmune disorder, in which a person's immune system attacks the hair follicles. Genetic factors may contribute to AU as approximately 20% of those affected have a family member with alopecia.

Keratosis pilaris atrophicans faciei (also known as "Folliculitis rubra," "Keratosis pilaris rubra atrophicans faciei," "Lichen pilare," "Lichen pilaire ou xerodermie pilaire symetrique de la face," "Ulerythema ophryogenes," and "Xerodermie pilaire symetrique de la face") begins in infancy as follicular papules with perifollicular erythema. Initially, the lesions are restricted to the lateral eyebrows, but with time spread to involve the cheeks and forehead, and may also be associated with keratosis pilaris on the extremities and buttocks.

Seborrhea affects 1 to 5% of the general population. It is slightly more common in men, but affected women tend to have more severe symptoms. The condition usually recurs throughout a person's lifetime. Seborrhea can occur in any age group but usually starts at puberty and peaks in incidence at around 40 years of age. It can reportedly affect as many as 31% of older people. Severity is worse in dry climates.

There is no standard treatment for alopecia universalis. Many treatments have been explored, including immunomodulatory agents such as imiquimod. Tofacitinib citrate may also have benefits. In June 2014, it was reported that a 25 year old man with almost no hair on his body grew a full head of hair, and eyebrows, eyelashes, facial, armpit and other hair, following 8 months of treatment.

Certain hair shampoos and ointments visually thicken existing hair, without affecting the growth cycle. There have also been developments in the fashion industry with wig design. The fashion accessory has also been shown to be a source of psychological support for women undergoing chemotherapy, with cancer survivors in one study describing their wig as a "constant companion". Other studies in women have demonstrated a more mixed psychosocial impact of hairpiece use.

Specialized scalp tattoos can mimic the appearance of a short buzzed haircut.

Focal facial dermal dysplasia (FFDD) is a rare genetically heterogeneous group of disorders that are characterized by congenital bilateral scar like facial lesions, with or without associated facial anomalies. It is characterized by hairless lesions with fingerprint like puckering of the skin, especially at the temples, due to alternating bands of dermal and epidermal atrophy.

This condition is also known as Brauer syndrome (hereditary symmetrical aplastic nevi of temples, bitemporal aplasia cutis congenita, bitemporal aplasia cutis congenita: OMIM ) and Setleis syndrome (facial ectodermal dysplasia: OMIM ).

Oliver–McFarlane syndrome is a condition characterized by hypertrichosis of the eyebrows and eyelashes.

Keppen–Lubinsky syndrome (KPLBS) is an extremely rare congenital disorder.The minimal clinical criteria for the Keppen–Lubinsky syndrome are as follows: normal growth parameters at birth, postnatal growth failure, peculiar face with an aged appearance (large prominent eyes, a narrow nasal bridge, a tented upper lip, a high palate, an open mouth), skin tightly adherent to facial bones, generalized lipodystrophy, microcephaly, and development delay. Keppen-Lubinsky syndrome is caused by mutation in the inwardly rectifying K+ channels encoded by KCNJ6 gene.

Kleefstra syndrome affects males and females equally and approximately, 75% of all documented cases are caused by Eu-HMTase1 disruptions while only 25% are caused by 9q34.3 deletions. There are no statistics on the effect the disease has on life expectancy due to the lack of information available.