An acanthoma is a skin neoplasm composed of squamous or epidermal cells. It is located in the prickle cell layer.

Types of acanthoma include pilar sheath acanthoma, a benign follicular tumor usually of the upper lip; clear cell acanthoma, a benign tumor found most frequently on the legs; and Degos acanthoma, often confused with but unrelated to Degos disease.

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.

A port-wine stain (nevus flammeus), also commonly called a firemark, is a discoloration of the human skin caused by a vascular anomaly (a capillary malformation in the skin). They are so named for their coloration, which is similar in color to port wine, a fortified red wine from Portugal.

A port-wine stain is almost always a birthmark; in rare cases it can develop in early childhood. Either way, port-wine stains ordinarily persist throughout life. The area of skin affected grows in proportion to general growth.

Port-wine stains occur most often on the face but can appear anywhere on the body, particularly on the neck and upper trunk. Early stains are usually flat and pink in appearance. As the child matures, the color may deepen to a dark red or purplish color. In adulthood, thickening of the lesion or the development of small lumps may occur.

Port-wine stains may be part of a syndrome such as Sturge–Weber syndrome or Klippel–Trénaunay–Weber syndrome.

Nevus flammeus may be divided as follows:

- Nevus flammeus nuchae

- Midline nevus flammeus

The most common eyelid tumor is called basal cell carcinoma. This tumor can grow around the eye but rarely spreads to other parts of the body. Other types of common eyelid cancers include squamous carcinoma, sebaceous carcinoma and malignant melanoma. The most common orbital malignancy is "orbital lymphoma". This tumor can be diagnosed by biopsy with histopathologic and immunohistochemical analysis. Most patients with orbital lymphoma can be offered chemotherapy or radiation therapy.

Rhinophyma is a slowly progressive condition due to hypertrophy of the sebaceous glands of the tip of the nose often seen in cases of long-standing acne rosacea; it is not a neoplasm. It presents as a pink, lobulated mass over the nose with superficial vascular dilation; it mostly affects men past middle age. Patients seek advice because of the perceived unsightly appearance of the enlargement, or obstruction in breathing and vision.

Trichoepithelioma is a neoplasm of the adnexa of the skin. Its appearance is similar to basal cell carcinoma.

One form has been mapped to chromosome 9p21.

The appearance and number of sarcoids can vary, with some horses having single or multiple lesions, usually on the head, legs, ventrum and genitalia or around a wound. The distribution pattern suggests that flies are an important factor in the formation of sarcoids. Sarcoids may resemble warts (verrucous form), small nodules (nodular form), oval hairless or scaly plaques (occult form) or very rarely, large ulcerated masses (fibroblastic form). The occult form usually presents on skin around the mouth, eyes or neck, while nodular and verrucous sarcoids are common on the groin, penile sheath or face. Fibroblastic sarcoids have a predilection for the legs, groin, eyelid and sites of previous injury. Multiple forms may also be present on an individual horse (mixed form). Histologically, sarcoids are composed of fibroblasts (collagen producing cells) that invade and proliferate within the dermis and sometimes the subcutaneous tissue but do not readily metastasize to other organs. Surgical biopsy can definitively diagnose sarcoids, but there is a significant risk of making sarcoids worse. Therefore, diagnosis based solely on clinical signs, fine-needle aspiration or complete excisional biopsy are safer choices.

Rhinophyma is characterised by prominent pores and a fibrous thickening of the nose, sometimes with papules. It is associated with the common skin condition rosacea. It can carry a strong psychological impact due to its effect on one's personal appearance.

The most common sites for melanotic tumors are on the under-side of the tail near the base, on the prepuce, around the mouth or in the skin over the parotid gland (near the base of the ear). Tumors will initially begin as single, small raised areas that may multiply or coalesce into multi-lobed masses (a process called melanomatosis) over time. Horses under 2-years-old can be born with or acquire benign melanotic tumors (called melanocytomas), but these tumors are often located on the legs or trunk, not beneath the tail as in older animals.

Hidrocystoma (also known as cystadenoma, a Moll's gland cyst, and a sudoriferous cyst) is an adenoma of the sweat glands.

Hidrocystomas are cysts of sweat ducts, usually on the eyelids. They are not tumours (a similar-sounding lesion called hidroadenoma is a benign tumour).

There are three types of "sweat" glands: True sweat glands or eccrine glands;

sebaceous glands, which have an oily secretion around hair follicles; and apocrine glands which have more oily product than eccrine glands and are found on the face, armpit, and groin.

Hidrocystomas usually arise from apocrine glands. They are also called Cysts of Moll or sudoriferous cysts. There may be a type of hidroadenoma that arises from eccrine glands, but these are uncommon.

Other related conditions on the eyelids include chalazion ( a granulomatous reaction to sebaceous glands on the eyelid), lacrimal duct cysts (cysts related to tear ducts) and nasolacrimal duct cysts (the nasolacrimal duct drains tears into the nose via a punctum on the lower eyelid).

Conjunctival concretions are generally asymptomatic. Common symptoms include eye discomfort, eye irritation, and foreign body sensation. Sometimes, the larger, harder or multiple concretions make the rubbing off of the superficial layers of the conjunctiva or eyelids to cause conjunctival abrasion, especially prominent when upon blinking. In severe cases, dysfunction or inflammation of the Meibomian (Meibomianitis, an inflammation of the tarsal glands) glands may occur.

Sebaceous carcinoma is an uncommon and aggressive malignant cutaneous tumor. Most are typically about 10 mm in size at presentation. This neoplasm is thought to arise from sebaceous glands in the skin and, therefore, may originate anywhere in the body where these glands are found. Because the periocular region is rich in this type of gland, this region is a common site of origin. The cause of these lesions are, in the vast majority of cases, unknown. Occasional cases may be associated with Muir-Torre syndrome.

This type of cancer usually has a poor prognosis because of a high rate of metastasis.

Symptoms are not specific; most patients report itching, burning, and soreness. A small subset of patients may be asymptomatic. Presence of vulvar pain, bleeding, and tumor formation are reported to be more common in patients affected by invasive disease.Signs and symptoms are skin lesions, often mistaken as eczema, that may be itchy or painful.

Vulvar Paget disease presents as a variety of clinical lesions that may occur over a protracted course. Initially it is velvety, soft, and red or bright pink with scattered white islands of hyperkeratosis. (a strawberry and cream appearance) The lesions become erythematous, plaque like, and desquamating especially when located in dry areas. Rarely the appearance is ulcerated. The borders appear irregular, slightly elevated, and sharply demarcated. The visible borders of vulvar Paget disease are often misleading as Paget cells may spread along the basal layers of normal appearing skin with multicentric foci. Involvement may be extensive including the perianal region, genitocrural, and inguinal folds. Clinical examination should determine the presence of periurethral and perianal lesions. In these cases an involvement of the skin by a noncutaneous internal neoplasm may occur.

Schöpf–Schulz–Passarge syndrome (also known as "eyelid cysts, palmoplantar keratoderma, hypodontia, and hypotrichosis") is an autosomal recessive condition with diffuse symmetric palmoplantar keratoderma, with the palmoplantar keratoderma and fragility of the nails beginning around age 12. In addition to palmoplantar keratoderma, other symptoms include hypodontia, hypotrichosis, nail dystrophies, and eyelid cysts (apocrine hidrocystomas). Patients may also develop syringofibroadenoma and squamous cell carcinomas.

It was characterized in 1971.

It has been associated with WNT10A.

Chronic conjunctivitis (e.g. trachoma) and aging factor are two causes of conjunctival concretion, which will make the conjunctiva cellular degeneration to produce an epithelial inclusion cyst, filled with epithelial cells and keratin debris. After calcification, the conjunctival cyst hardens and forms a conjunctival concretion. Congenital conjunctival concretion condition is also more common.

Trichoepitheliomas consisted of nests of basaloid cells. They lack the myxoid stroma and artefactual clefting seen in basal cell carcinoma. Mitoses are uncommon when compared to basal cell carcinoma.

These terms are related since they represent the steps of the progression toward cancer:

- Dysplasia is the earliest form of precancerous lesion recognizable in a biopsy. Dysplasia can be low-grade or high-grade. High-grade dysplasia may also be referred to as carcinoma "in situ".

- Invasive carcinoma, usually simply called cancer, has the potential to invade and spread to surrounding tissues and structures, and may eventually be lethal.

Ectropion is a medical condition in which the lower eyelid turns outwards. It is one of the notable aspects of newborns exhibiting congenital Harlequin-type ichthyosis, but ectropion can occur due to any weakening of tissue of the lower eyelid. The condition can be repaired surgically. Ectropion is also found in dogs as a genetic disorder in certain breeds.

Well-differentiated and moderately differentiated sebaceous carcinoma tend to exhibit vacuolization within the cytoplasm of the tumor cells. Histology may mimic basal cell carcinoma.

Complications of blepharochalasis may include conjunctival hyperemia (excessive blood flow through the moist tissues of the orbit), chemosis, entropion, ectropion, and ptosis.

A distichia is an eyelash that arises from an abnormal spot on the eyelid. This abnormality, attributed to a genetic mutation, is known to affect dogs and humans. Distichiae (the abnormal eyelash) usually exit from the duct of the meibomian gland at the eyelid margin. They are usually multiple and sometimes more than one arises from a duct. They can affect either the upper or lower eyelid and are usually bilateral. The lower eyelids of dogs usually have no eyelashes.

Distichiae usually cause no symptoms because the lashes are soft, but they can irritate the eye and cause tearing, squinting, inflammation, and corneal ulcers and scarring. Treatment options include manual removal, electrolysis, electrocautery, cryotherapy, and surgery.

Ectropion in dogs usually involves the lower eyelid. Often the condition has no symptoms, but tearing and conjunctivitis may be seen. Breeds associated with ectropion include the Cocker Spaniel, the Saint Bernard, the Bloodhound, the Clumber Spaniel, and the Basset Hound. It can also result from trauma or nerve damage. Treatment (surgery) is recommended only if there is chronic conjunctivitis or if there is corneal damage. A small part of the affected lid is removed and then the lid is sewn back together.

Blepharochalasis results from recurrent bouts of painless eyelid swelling, each lasting for several days. This is thought to be a form of localized angioedema, or rapid accumulation of fluid in the tissues. Recurrent episodes lead to thin and atrophic skin. Damage to the levator palpebrae superioris muscle causes ptosis, or drooping of the eyelid, when the muscle can no longer hold the eyelid up.