Ultraviolet radiation from sun exposure is the primary environmental cause of skin cancer. Other risk factors that play a role include:

- Smoking tobacco

- HPV infections increase the risk of squamous-cell skin cancer.

- Some genetic syndromes including congenital melanocytic nevi syndrome which is characterized by the presence of nevi (birthmarks or moles) of varying size which are either present at birth, or appear within 6 months of birth. Nevi larger than 20 mm (3/4") in size are at higher risk for becoming cancerous.

- Chronic non-healing wounds. These are called Marjolin's ulcers based on their appearance, and can develop into squamous-cell skin cancer.

- Ionizing radiation such as X-rays, environmental carcinogens, artificial UV radiation (e.g. tanning beds), aging, and light skin color. It is believed that tanning beds are the cause of hundreds of thousands of basal and squamous-cell skin cancer. The World Health Organization now places people who use artificial tanning beds in its highest risk category for skin cancer. Alcohol consumption, specifically excessive drinking increase the risk of sunburns.

- The use of many immunosuppressive medications increases the risk of skin cancer. Cyclosporin A, a calcineurin inhibitor for example increases the risk approximately 200 times, and azathioprine about 60 times.

Lymphoma is the most common type of blood-related cancer in horses and while it can affect horses of all ages, it typically occurs in horses aged 4–11 years.

The mortality rate of basal-cell and squamous-cell carcinoma are around 0.3%, causing 2000 deaths per year in the US. In comparison, the mortality rate of melanoma is 15–20% and it causes 6500 deaths per year. Even though it is much less common, malignant melanoma is responsible for 75% of all skin cancer-related deaths.

The survival rate for people with melanoma depends upon when they start treatment. The cure rate is very high when melanoma is detected in early stages, when it can easily be removed surgically. The prognosis is less favorable if the melanoma has spread to other parts of the body. As of 2003 the overall five year cure rate with Mohs' micrographic surgery was around 95 percent for recurrent basal cell carcinoma.

Australia and New Zealand exhibit one of the highest rates of skin cancer incidence in the world, almost four times the rates registered in the United States, the UK and Canada. Around 434,000 people receive treatment for non-melanoma skin cancers and 10,300 are treated for melanoma. Melanoma is the most common type of cancer in people between 15–44 years in both countries. The incidence of skin cancer has been increasing. The incidence of melanoma among Auckland residents of European descent in 1995 was 77.7 cases per 100,000 people per year, and was predicted to increase in the 21st century because of "the effect of local stratospheric ozone depletion and the time lag from sun exposure to melanoma development."

The incidence of squamous cell carcinoma continues to rise around the world. A recent study estimated that there are between 180,000 and 400,000 cases of SCC in the United States in 2013. Risk factors for squamous cell carcinoma varies with age, gender, race, geography, and genetics. The incidence of SCC increases with age and the peak incidence is usually around 60 years old. Males are affected with SCC at a ratio of 2:1 in comparison to females. Caucasians are more likely to be affected, especially those with fair Celtic skin and chronically exposed to UV radiation. Squamous cell carcinoma of the skin is the most common among all sites of the body. Solid organ transplant recipients (heart, lung, liver, pancreas, among others) are also at a heightened risk of developing aggressive, high-risk SCC. There are also a few rare congenital diseases predisposed to cutaneous malignancy. In certain geographic locations, exposure to arsenic in well water or from industrial sources may significantly increase the risk of SCC.

People who have received solid organ transplants are at a significantly increased risk of developing squamous cell carcinoma due to the use of chronic immunosuppressive medication. While the risk of developing all skin cancers increases with these medications, this effect is particularly severe for SCC, with hazard ratios as high as 250 being reported, versus 40 for basal cell carcinoma. The incidence of SCC development increases with time posttransplant. Heart and lung transplant recipients are at the highest risk of developing SCC due to more intensive immunosuppressive medications used. Squamous cell cancers of the skin in individuals on immunotherapy or suffering from lymphoproliferative disorders (i.e. leukemia) tend to be much more aggressive, regardless of their location. The risk of SCC, and non-melanoma skin cancers generally, varies with the immunosuppressive drug regimen chosen. The risk is greatest with calcineurin inhibitors like cyclosporine and tacrolimus, and least with mTOR inhibitors, such as sirolimus and everolimus. The antimetabolites azathioprine and mycophenolic acid have an intermediate risk profile.

Tumors related to squamous-cell carcinoma (SCC) can appear anywhere on the body, but they are most often located in non-pigmented skin near mucocutaneous junctions (where skin meets mucous membranes) such as on the eyelids, around the nostrils, lips, vulva, prepuce, penis or anus. The tumors are raised, fleshy, often ulcerated or infected and may have an irregular surface. Rarely, primary SCC develops in the esophagus, stomach (non-glandular portion), nasal passages and sinuses, the hard palate, gums, guttural pouches and lung. The eyelid is the most common site, accounting for 40-50% of cases, followed by male (25-10% of cases) and female (10% of cases) genitalia. Horses with lightly pigmented skin, such as those with a gray hair coat or white faces, are especially prone to developing SCC, and some breeds, such as Clydesdales, may have a genetic predisposition. Exposure of light-colored skin to UV light has often been cited as a predisposing factor, but lesions can occur in dark skin and in areas that are not usually exposed to sunlight, such as around the anus. Buildup of smegma ("the bean" in horseman's terms) on the penis is also linked to SCC and is thought to be a carcinogen through penile irritation. Pony geldings and work horses are more prone to developing SCC on the penis, due to less frequent penile washing when compared to stallions. Equine papillomavirus-2 has also been found within penile SCCs, but has not been determined to cause SCC.

Basal-cell carcinoma is a common skin cancer and occurs mainly in fair-skinned patients with a family history of this cancer. Sunlight is a factor in about two-thirds of these cancers; therefore, doctors recommend sunscreens with at least SPF 30. One-third occur in non-sun-exposed areas; thus, the pathogenesis is more complex than UV exposure as "the" cause.

The use of a chemotherapeutic agent such as 5-Fluorouracil or imiquimod, can prevent development of skin cancer. It is usually recommended to individuals with extensive sun damage, history of multiple skin cancers, or rudimentary forms of cancer (i.e., solar keratosis). It is often repeated every 2 to 3 years to further decrease the risk of skin cancer.

The etiology of florid cutaneous papillomatosis is unknown. It is likely directly induced by an underlying neoplasm secreting a growth factor. One candidate may be alpha-transforming growth factor, structurally related to epidermal growth factor, but antigenically distinct from it. The underlying cancer is most often gastric adenocarcinoma but also with breast cancer, bladder cancer, hepatobiliary cancer, ovarian cancer, uterine cancer, prostate cancer, lung cancer and cervical cancer. Other associated underlying malignancies include squamous cell carcinomas and lymphomas.

Florid cutaneous papillomatosis is almost twice as common in men than in women, and is usually diagnosed in individuals aged 53–72 years (mean patient age, 58.5 years).

Basal-cell cancer is a very common skin cancer. It is much more common in fair-skinned individuals with a family history of basal-cell cancer and increases in incidence closer to the equator or at higher altitude. There are approximately 800,000 new cases yearly in the United States alone. Up to 30% of Caucasians develop basal-cell carcinomas in their lifetime. In Canada, the most common skin cancer is basal cell carcinoma (as much as one third of all cancer diagnoses), affecting 1 in 7 individuals over a lifetime.

In the United States approximately 3 out of 10 caucasians develop a basal cell carcinoma during their lifetime. This tumor accounts for approximately 70% of non-melanoma skin cancers. In 80 percent of all cases, basal cell carcinoma affects the skin of head and neck. Furthermore, there appears to be an increase in the incidence of basal-cell cancer of the trunk in recent years.

Most sporadic BCC arises in small numbers on sun-exposed skin of people over age 50, although younger people may also be affected. The development of multiple basal-cell cancer at an early age could be indicative of nevoid basal-cell carcinoma syndrome, also known as Gorlin's Syndrome.

It occurs in all adult age groups. While the majority of patients are between 40 and 59 years old, age predilection is much less pronounced than in noninflammatory breast cancer. The overall rate is 1.3 cases per 100000, black women (1.6) have the highest rate, Asian and Pacific Islander women the lowest (0.7) rates.

Most known breast cancer risk predictors do not apply for inflammatory breast cancer. It may be slightly associated with cumulative breast-feeding duration.

Most patients diagnosed with Paget's disease of the nipple are over age 50, but rare cases have been diagnosed in patients in their 20s. The average age at diagnosis is 62 for women and 69 for men. The disease is rare among both women and men.

The saree is common female attire in the Indian subcontinent. It is a piece of long (generally ) cloth which can be made of various materials: cotton, silk, nylon, chiffon or synthetic fabric. It is worn over an inner skirt (petticoat) which is tightened around the waist by a thick cotton cord. This is the traditional costume of most Indian women. The saree is attached to the waist throughout the day in the hot and humid climate. The waist is often soiled with dust and sweat and remains without proper cleaning. This causes changes in pigmentation and mild scaling over the waist. This, in turn, causes chronic irritation and gradually malignancy may develop in the skin at the waistline.

Studies have recorded an incidence of about 3–5 cases per 1,000 newborn babies.

Saree cancer is a type of skin cancer that occurs along the waistline in females wearing the saree, caused by constant irritation which can result in scaling and changes in pigmentation of the skin. It is a rare type of cancer and generally found in the Indian subcontinent, where sarees are commonly worn by girls and women throughout their lives. It is similar to Marjolin's ulcer in cause, involving chronic inflammation.

The presence of three factors for the prognosis has been suggested, whether there is a palpable mass of the disease, whether lymph nodes are positive and whether there is an underlying malignant cancer.

If there is none of these, the five- and 10-year survival is 85% and 80% respectively, with adjuvant chemotherapy even 95% and 90%. If there is a palpable mass, it is 32% and 31% respectively, with adjuvant chemotherapy (40% and 35%).

Positive lymph-nodes have been positively associated with a palpable mass and affect the prognosis to be now just 28% survival after 10 years (vs 79% without palpable mass and without affected lymph-nodes). Involvement of the lymph nodes does not directly cause any harm, but is merely an indicator of systemic spread.

Furthermore, patients with an identifiable associated underlying breast tumor have a survival rate of 38-40% at five years and a survival rate of 22-33% at 10 years. The death rate of metastatic breast carcinoma in patients with mammary Paget's disease and underlying cancer is 61.3%, with a 10-year cumulative survival rate of 33%.

Port-wine stains were shown to be caused by a somatic activating c.548G→A mutation in the GNAQ gene. An association with RASA1 has also been described.

Orbital dermoid cysts are benign which are typically found at the junction of sutures, most commonly at the fronto-zygomatic suture. Large deep orbital dermoid cysts can cause pressure effects on the muscles and optic nerve, leading to diplopia and loss of vision.

Age distribution and relation to breastfeeding duration is suggestive of some sort of involvement of hormones in the aetiology, however significant differences exist compared to normal breast cancer.

Typically IBC shows low levels of estrogen and progesterone receptor sensitivity, corresponding with poor outcome. In cases with positive estrogen receptor status antihormonal treatment is believed to improve outcome.

Paradoxically some findings suggest that especially aggressive phenotypes of IBC are characterised by high level of NF kappaB target gene expression which can be - under laboratory conditions - successfully modulated by estrogen, but not by tamoxifen.

An ectopic cilia is a special type of distichia. It is usually found in younger dogs. Commonly affected breeds include Poodles, Golden Retrievers, and Shih Tzus. The eyelash exits through the conjunctiva of the eyelid facing toward the eye, usually at the middle of the upper eyelid. It can cause intense pain and corneal ulcers. Treatment is surgery or cryotherapy.

Dermatochalasis commonly affects the elderly, although sometimes it is congenitally acquired. The elderly version may begin to develop as early as 40 years of age, and it continues to progress with age. The congenital version may begin around 20 years of age. There is no racial predisposition towards developing dermatochalasis, and men and women are equally affected.

Many types of skin tumors, both benign (noncancerous) and malignant (cancerous), exist. Approximately 20-40% of primary skin tumors are malignant in dogs and 50-65%

are malignant in cats. Not all forms of skin cancer in cats and dogs are caused by sun exposure, but it can happen occasionally. On dogs, the nose and pads of the feet contain sensitive skin and no fur to protect from the sun. Also, cats and dogs with thin or light-colored coats are at a higher risk of sun damage over their entire bodies.

There is currently researching being done to find more treatments dependent on the different pre-existing conditions.

Studies are being conducted in which madarosis can be related to malignancy. A study by Groehler and Rose found that there was a statistical significance between these two. They concluded that patients malignancy lesions on the eyelid have a higher chance of having madarosis than a patient with a benign lesion. They stated that despite the fact that it is significant, the absence of madarosis does not mean the lesion cannot be malignant.

In many leprosy cases, madarosis is a symptom or a quality after diagnosis. However, in India, leprosy is common and researchers report a case of madarosis before diagnosis of leprosy with no skin lesions, only madarosis. This allowed for quicker treatment.

A main reason many people have madarosis is due to the chemotherapy drugs. There was a clinical trial in 2011 that tested an eyelash gel called bimatoprost. This gel enhanced the eyelashes in quantity and thickness. They tested this on 20 breast cancer patients who were undergoing chemotherapy. Results seemed positive, in that the group of people who used the gel had growth of eyelashes after the chemotherapy drugs.

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.

Styes are most commonly caused by the blocking of an oil gland at the base of the eyelash. Styes are experienced by people of all ages. Styes can be triggered by poor nutrition, sleep deprivation, lack of hygiene, lack of water, and rubbing of the eyes. Styes often result from a Staphylococcal infection in the eye, and can be secondary to blepharitis or a deficiency in immunoglobulin. Sharing of washcloths or face towels should be curtailed to avoid spreading the infection between individuals. Styes can last from one to two weeks without treatment, or as little as four days if treated properly.