A
Abscess: A collection of white blood cells in the skin, hair follicles, sweat glands or subcutaneous tissue.
Acne: A general term for local skin inflammation caused by overactivity of sebaceous glands and clogging of skin pores, usually on the face, neck, back, shoulders and chest. Acne can mean comedones such as blackheads and whiteheads, or severe inflammation such as nodules and cysts.
Acne conglobata: A severe type of acne wherein nodules are connected to each other and to acne lesions below the epidermis.
Acne mechanica: A form of acne caused by pressure on the skin, covering the skin, heat and/or frequent rubbing or abrasions against the skin.
Acne vulgaris: The most common form of acne, characterized by the presence of blackheads, whiteheads, pustules and/or papules.
Actinic keratosis: A form of acne in which small, reddish patches appear on the skin. Patches are often rough. This form of acne is more common in fair skin, and can become cancerous if left untreated.
Androgens: Hormones, present in males and females, which stimulate the production of sebum (oil). Androgen levels are higher in males than in females, and are responsible for physical maturity in males.
Antibacterial: Refers to agents that destroy or decrease the growth or multiplication of bacteria. Antiobiotics, chlorine and heat are some examples of antibacterial agents. Antibacterial agents suppress symptoms of bacterial diseases but do not reduce the risk of viral infections.
Antibiotics: Drugs used to treat bacterial infections and destroy or suppress the growth of other microorganisms.
Antimicrobial: Refers to agents that destroy microorganisms in the body.

B
Bacteria: Single-cell micro-organisms that can exist as free-living, independent organisms or as parasites.
Blackhead: An acne lesion filled with excess dead skin cells and oil. Blackheads are non-inflammatory. They are also known as “open comedones” because the surface of the skin remains open.
Blister: A fluid-filled cavity. Fluid may be tissue fluid, blood or plasma. Blisters are inflammatory. Also known as vesicle or bulla.
Boil: Lesion that forms around follicles as a result of infection or inflammation. Boils are painful and swollen. Also known as furuncle.

C
Chloracne: A type of rash in which many comedones develop due to exposure to chlorinated chemicals and/or herbicides.
Closed comedo: A whitehead; a non-inflammatory comedo where the surface of the skin is closed.
Collagen: A fibrous protein that provides strength and elasticity to skin, tissue, tendons, cartilage, ligaments and bones.
Comedo (pl. comedones): The primary manifestation of acne, an acne lesion that consists of an expanded hair follicle filled with oil, bacteria and dirt. Comedones may be closed or open.
Comedogenic: Likely to cause or aggravate acne.
Cortico-steroids: Synthetic hormones that are similar to the cortisone hormone produced by the adrenal cortex. Cortico-steroids are available in the form of pills, injections and tropical treatments.
Cortisone: A hormone naturally produced and secreted by the adrenal gland. Also used as anti-inflammatory medication.
Cyst: A deep, painful, fluid-filled nodule. Cysts are small, yellowish and round elevations below the epidermis, and can expand and infect to cause scarring, if left untreated. Acne cysts are one type of cysts caused or made worse by acne.

D
Dehydrated skin: Skin lacking in moisture.
Dermis: The sensitive layer of the skin between the epidermis and the sub cutis. Dermis contains blood vessels, lymph vessels, hair follicles, nerve endings, sweat glands, sebacious glands and connective tissue.
Dry skin: Skin lacking in natural oil (sebum).

E
Epidermis: The outermost layer of the skin.
Eruptions: Skin lesions that are raised, conspicuous and often inflamed.
Essential Fatty Acids: The basic components of cellular membrane, required for human metabolism. Essential fatty acids cannot be synthesized within the body and must be consumed from diet. Omega 3, Omega 6, Flaxseed, and Goji Berry are some essential fatty acids.
Essential oils: Aromatic oils extracted from plants. Essential oils have therapeutic and healing properties.
Exfoliation: The removal or peeling off of the top layer of epidermis by mechanical or chemical methods in order to shed skin debris and unclog the pores of the skin. Gentle exfoliation may be done by a scrubbing cleanser or a topical treatment. Severe or chemical exfoliation may be performed by dermatologists in order to treat acne.

F
Follicle: A small cavity or sac, lined by the epidermis, through which the hair grows, and where sebum (oil) is discharged by the sebaceous gland into the surface of the skin.
Folliculitis: A painful condition characterized by cystic nodules, when hair is trapped within the follicle.
Follicular Lumen: The canal of the hair follicle, into which the sebaceous gland secretes sebum.
Free Radicals: Unstable molecules which occur naturally in living beings and in the environment, and are the main cause of ageing. Free radicals react with other chemicals in the body and interfere with natural cell factions.

G
Gland: An organ that synthesizes substances essential for the body and secretes them through ducts or cavities, or directly into the bloodstream. Sebaceous gland and thyroid gland are two examples.

H
Hair follicle: See follicle, above.
Hormone: A chemical substance produced by the body that governs and regulates certain body processes. Androgens are hormones which are responsible for physical growth during puberty, and have been linked to teenage acne.
Hypertrophic Scar: A scar at the site of a wound caused as a result of excessive collagen deposits.

I
Infection: The growth and multiplication of parasitic organisms within the body. Parasites draw their nourishment from the host, grow, and have adverse affects on the host body.
Inflammation: A bodily reaction to infection, injury or other irritation. Inflammation is non-specific immune response characterized by redness, heat, pain and swelling. .
Inflammatory: Causing inflammation. In relation to acne, inflammatory lesions are those wherein the skin surface is inflamed by chemical reactions or bacteria clogging the hair follicles.
Isotretinoin: Systemic medication used to treat severe cases of acne. Isotretinoin should not be taken by pregnant women or those trying to become pregnant.

K
Keloid: Raised, pinkish scar resulting from excessive tissue repair that spreads beyond the original area of injury.

L
Lesion: An area of abnormal tissue caused by disease or trauma. In relation to acne, lesions are caused as a result of infection in the pilosebaceous unit.
Lipids: Any of a group of organic compounds including fat and fat-like substances characterized by insolubility in water and solubility in fat solvents. Sebum is comprised of lipids. Free fatty acids are a particular type of lipids that irritate the skin.

M
Macule: A flat spot or patch of skin that is not the same color as the surrounding skin.
Melanin: Insoluble pigment responsible for the color of hair and skin.
Microcomedo: The initial stage of comedo formation, where the comedo can only be discerned under a microscope.

N
Nodule: A small, rounded bump or node that can be felt by touch. Acne nodules are deep, firm and inflamed.
Nodulocystic acne: A severe acne condition where nodules and cysts are both present, and are characterized by deep inflammation and scarring after healing.
Noncomedogenic: Unlikely to cause acne. People suffering from acne are recommended the use of noncomedogenic cosmetics and cleansers.
Non-inflammatory: Comedones that are not accompanied by redness, inflammation or pain.
Normal/combination skin: Skin that is partially oily and partially dry. The t-zone (the forehead, nose and chin) is often oily, while the cheeks and jaw are dry.

O
Open comedo: A non-inflammatory comedo characterized by a firm and dark elevation, where the surface of the inflamed skin remains open. Blackheads are open comedones.
Oily skin: Skin characterized by an excess of oil production by the sebaceous gland.

P
Papule: An inflamed comedo or skin elevation characterized by redness and firmness. Distinguished from pustules by the absence of pus.
Papulopustular: Refers to acne characterized by the presence of pustules and papules.
Pilosebaceous Unit: A unit consisted of hair, hair follicle and sebaceous gland.
Pimples: Small papules or pustules.
Post-inflammatory hyper-pigmentation: A condition characterized by the darkening of skin in places where it was previously inflamed.
Propionibacterium acnes: Also known as P. acnes. A naturally occurring bacteria that multiplies rapidly in those hair follicles where sebum is trapped, leading to acne. It is also associated with allergic alveolitis, cholesterol gallstones, corneal ulcers, endocarditis, pulmonary angiitis, sarcoidosis, and the SAPHO syndrome.
Puberty: The period of time in which a child transitions into adulthood. This period is characterized by hormonal secretions, reproductive functionality, development of secondary sexual characteristics and growth spurts. Due to increased hormone production, puberty is the most common period of acne outbreaks.
Pus: A whitish, yellowish or yellow-brownish substance produced as a result of the body’s inflammatory response to infection. Pus is a mixture of dead skin cells, white blood cells and bacteria.
Pustule: An inflamed comedo with a white, pus-filled center and a ring of redness around it.

R
Rash: Eruption or breaking out of the skin, characterized by a change in color, appearance or texture. Medically known as exanthem.
Retinoid: A class of chemical compounds related chemically to or derived from vitamin A. Retinoids may be natural or synthetic.
Retinol: A derivative of Vitamin A, retinol is a fat soluble carotenoid substance that helps to stabilize the production of skin cells. It is commonly used as an anti-ageing and anti-acne treatment.
Rosacea: A type of skin disease that occurs mostly in adults. It is a chronic form of acne characterized by redness, papules, and may also thicken the skin over time. Rosacea is often called “adult acne”. Women are more prone to rosacea.

S
Scar: An area of fibrous tissue that replaces skin (or other tissue) after an injury or wound, as part of the biologic process of repair.
Sebaceous glands: Glands that secrete sebum into the surface of the skin. Sebacious glands are attached to hair follicles and found mostly on the face, neck, back and chest. Acne lesions occur in sebacious glands.
Sebum: An oily substance produced by sebacious glands. Sebum preserves the moisture and flexibility of skin and hair.
Steroid acne: Acne caused by the excessive use of cortico-steroid treatments. For this reason cortico-steroids are prescribed for a limited period only.
Sub cutis: The subcutaneous layer of the skin, which lies below the dermis.
Sunscreen: A cream or lotion which contains a chemical (PABA) to protect the skin against sunburn and skin damage by absorbing ultraviolet rays. The strength of this protection is measured in terms of SPF. Sunscreen is different from sunblock in that the latter deflects sun rays whereas sunscreen absorbs them.
Systemic therapy: Therapy that involves the internal consumption of medication. Pills, injections and infusions are types of systemic therapy.

T
Topical: Localized, as in treatment pertaining to a specific area of the skin. Topical agents are designed to treat only the particular areas of skin onto which they are applied. If topical agents are absorbed inadvertently into the blood stream, their effects may be widespread and undesirable.
Toner: Cleansing product applied usually after the use of cosmetics to remove dirt and restore the skin’s normal pH.

V
Vitamin A: A family of similarly-structured molecules known as retinoids. The body converts carotene compounds (which occur naturally in substances such as egg yolk and milk) into vitamin A (retinol).
Vesicle: A cavity filled with clear fluid, a small blister.

W
White blood cells: Component cells of the immune system which help the body fight infections and foreign substances.
Whitehead: An acne lesion caused due to the blockage of follicles by oil and dead skin cells. Whiteheads are also called ‘closed comedones’ because the surface of the skin is closed due to clogging.