Blepharitis: Inflammation of the eyelids.

Cathelicidins: A type of antimicrobial molecule that is part of the innate immune system’s response to infection, and plays a role in the inflammation associated with rosacea.

Chalazion: A cyst on the eyelid due to plugging of the meibomian glands, fat-secreting glands of the eyes.

Comedone: A plugged hair follicle. May be open (blackhead) or nearly closed (whitehead).

Comorbidity: The occurrence of two disorders or illnesses in the same person, at the same time or one after another. Comorbidity does not necessarily mean that one causes the other.

Controlled study: An experiment or clinical trial that includes an untested comparison group, referred to as a "control group."

Cutaneous: Pertaining to the skin.

Demodex mites: Microscopic mites that are a normal inhabitant of human facial skin and eyelashes, but are often found in greater numbers on the skin of rosacea patients. Whether the higher incidence is a cause or result of the disease has not been determined.

Double-blind: A research procedure in which neither the patient nor the investigator knows who is receiving the experimental substance or procedure and who is receiving a placebo. Done to avoid bias in the study.

Edema: Swelling from abnormally large amounts of fluids in the tissues.

Erythema: Abnormal redness of the skin.

Erythematotelangiectatic rosacea: Formerly referred to as “subtype 1,” a common presentation of rosacea characterized by flushing and persistent redness. Visible blood vessels may also appear.

Flushing: Transient redness of the face and neck.

Granuloma: A tumor-like mass or nodule of tissue.

Granulomatous rosacea: Variant of rosacea, characterized by hard yellow, brown or red papules or nodules.

Innate immune system: The body’s first line of defense against infection, composed of a complex of immune cells that trigger one or more defense responses when they encounter bacteria, viruses or other pathogens.

Mast cells: A type of white blood cell located at the intersection of the nervous system and vascular system that is involved in the pathophysiology of rosacea.

Nasolabial folds: The creases or “laugh lines” that run from the nose to the corner of the mouth.

Neurovascular: Relating to or involving both the nerves and the blood vessels.

Nodule: A small node that is solid and can be detected by touch.

Ocular rosacea: Rosacea affecting the eyes, characterized by watery or bloodshot appearance, irritation, and/or burning or stinging. Formerly also referred to as “subtype 4.”

Papule: A small, dome-shaped, solid, usually inflamed elevation of the skin.

Papulopustular rosacea: Formerly also referred to as “subtype 2” rosacea, characterized by facial redness with bumps or pimples.

Paranasal: Alongside the nose.

Pathophysiology: The process or mechanisms by which a disease develops or progresses.

Phenotype: An observable characteristic that may result from a genetic or environmental influence, i.e., signs and symptoms of rosacea.

Phymatous rosacea: Formerly also referred to as “subtype 3” rosacea, characterized by thickening or growth of excess tissue, often around the nose.

Placebo: An oral or topical formulation without this active ingredient, used for comparison with the active medication in controlled clinical studies.

Plaque: Elevated red patch on the skin.

Pustule: A small elevation of the skin filled with a white substance.

Recalcitrant: Not responsive to treatment.

Rhinophyma: Enlargement of the nose with excess tissue, a common form of phymatous rosacea.

Subtype: A common pattern or grouping of signs and symptoms, are now considered outmoded. The classification of rosacea now focuses on individual signs and symptoms, or phenotypes.

Subtype 1 rosacea: Erythematotelangiectatic rosacea, characterized by flushing and persistent redness. Visible blood vessels may also appear.

Subtype 2 rosacea: Papulopustular rosacea, characterized by facial redness with bumps or pimples.

Subtype 3 rosacea: Phymatous rosacea, characterized by thickening or growth of excess tissue, often around the nose.

Subtype 4 rosacea: Ocular rosacea, characterized by watery or bloodshot appearance, irritation, burning or stinging of the eyes.

Telangiectasia: Small blood vessels visible through the skin.