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1. any of certain plants formed by the mutualistic combination of an alga and a fungus.
2. any of various papular skin diseases in which the lesions are typically small, firm papules set very close together.
lichen amyloido´sus a condition characterized by localized cutaneous amyloidosis.
lichen fibromucinoido´sus (lichen myxedemato´sus) a condition resembling myxedema but unassociated with hypothyroidism, marked by mucinosis and a widespread eruption of asymptomatic, soft, pale red or yellowish, discrete papules.
lichen ni´tidus a usually asymptomatic chronic inflammatory eruption consisting of numerous glistening, flat-topped, discrete, smooth, commonly skin-colored micropapules, located most often on the penis, lower abdomen, inner thighs, flexor aspects of the wrists and forearms, breasts, and buttocks. Widespread involvement may produce confluence of the lesions, with formation of scaly plaques.
lichen pila´ris lichen spinulosus.
lichen planopila´ris a variant of lichen planus characterized by formation of cone-shaped horny papules around the hair follicles, in addition to the typical lesions of ordinary lichen planus.
lichen pla´nus an inflammatory skin disease with wide, flat, purplish, shiny papules in circumscribed patches; it may involve the hair follicles, nails, and buccal mucosa; called also lichen ruber planus.
lichen ru´ber monilifor´mis a generalized or localized eruption with either round, dome-shaped, waxy, dark or bright red papules, or waxy, yellow, milia-like papules, often forming a moniliform (string-of-beads) pattern, sometimes arranged in keloidal bands. Some authorities consider the condition to be a variant of lichen simplex chronicus.
lichen ru´ber pla´nus lichen planus.
lichen sclero´sus (lichen sclero´sus et atro´phicus) a chronic atrophic skin disease marked by white papules with an erythematous halo and keratotic plugging. It sometimes affects the vulva (kraurosis vulvae) or penis (balanitis xerotica obliterans).
lichen scrofuloso´rum (lichen scrofulo´sus) a form of tuberculid manifested as an eruption of clusters of lichenoid papules on the trunk of children with tuberculous disease.
lichen sim´plex chro´nicus dermatosis of psychogenic origin, marked by a pruritic discrete, or more often, confluent lichenoid papular eruption, usually confined to a localized area. Mechanical trauma, such as scratching or rubbing the area, is a factor in its development. The lesions may arise from normal skin or they may occur as a complication of other forms of dermatitis. Called also circumscribed or localized neurodermatitis and lichen chronicum simplex.

Treatment consists of administration of corticosteroids applied locally as a cream or given by intralesional injection to relieve the pruritus. The area should be protected by light dressings and the patient encouraged to avoid mental stress, emotional upsets, and irritation of the affected area. The application of very hot or very cold compresses may afford temporary relief of the itching. The condition tends to become chronic with unexplained remissions and reappearance of lesions in a different part of the body.
lichen spinulo´sus a condition in which there is a horn or spine in the center of each hair follicle; called also lichen pilaris.
lichen stria´tus a self-limited condition characterized by a linear lichenoid eruption, usually in children.
lichen urtica´tus papular urticaria.
Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition. © 2003 by Saunders, an imprint of Elsevier, Inc. All rights reserved.


A discrete flat papule or an aggregate of papules giving a patterned configuration resembling lichen growing on rocks.
[G. leichēn, lichen; a lichenlike eruption]
Farlex Partner Medical Dictionary © Farlex 2012


1. A composite organism made up of a fungus, usually an ascomycete, that grows symbiotically with an alga or a cyanobacterium and characteristically forms a crustlike or branching growth on rocks or tree trunks.
2. Medicine Any of various skin diseases characterized by patchy eruptions of small, firm papules.
tr.v. li·chened, li·chening, li·chens
To cover with lichens.

li′chen·ous adj.
The American Heritage® Medical Dictionary Copyright © 2007, 2004 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.


A discrete flat papule or an aggregate of papules giving a patterned configuration resembling lichens growing on rocks.
[G. leichēn, lichen; a lichenlike eruption]
Medical Dictionary for the Health Professions and Nursing © Farlex 2012


(li'ken) [Gr. leichen, lichen]
1. Any form of papular skin disease, esp. lichen planus.
2. In botany, any of numerous plants consisting of a fungus growing symbiotically with algae. They form characteristic scaly or branching growths on rocks or barks of trees.

myxedematous lichen

Generalized eruption of asymptomatic nodules caused by mucinous deposits in the upper layers of the skin and in vessels and organs.

lichen nitidus

A rare skin condition characterized by small, chronic, asymptomatic papules that are usually pink and are usually located only on the penis, abdomen, and flexor surfaces of the elbows and palms.

lichen pilaris

Keratosis pilaris.

lichen planopilaris

A follicular papulosquamous eruption, typically found on the scalp, and often associated with lichen planus.
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lichen planus

An inflammatory rash marked by the presence of itchy, red to violet, polygon-shaped papules, which typically appear on the scalp, in the oral cavity, or on the limbs. The papules may merge into plaques crisscrossed by Wickham striae. Typically, the rash persists for 1 to 2 years and then spontaneously improves although about one in five patients will suffer a recurrence. Synonym: lichen ruber planus See: illustration


The cause of the rash is unknown, but it is occasionally associated with the use of chemicals (such as photoprocessing compounds, gold) or medications (such as beta blockers, diuretics, nonsteroidal anti-inflammatory drugs).


Corticosteroids, applied topically, taken orally, or injected into the lesions, are often effective.


lichen ruber moniliformis

Large verrucous lesions of lichen planus arranged like beads in a necklace.

lichen ruber planus

Lichen planus.
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lichen sclerosus et atrophicus

A chronic atrophic skin disorder marked by the appearance of discrete, flat-topped, white papules, which may coalesce and degenerate. The skin affected by the rash, which occurs most often on the vulva, is often thin, shiny, and scarred. Although this condition is not considered precancerous, squamous cell carcinomas arise in 1% to 5% of cases. See: illustration


Itching of the vulva, which may be intractable, is the most common complaint.


Potent topical corticosteroids produce remission, but not cure, in the great majority of patients.

Synonym: vulvar dystrophy; vulvar pruritus

lichen scrofulosus

An eruption of tiny punctate reddish-brown papules arranged in circles or groups in young people with tuberculosis. The lesions are caused by the spread of the tubercle bacilli through the blood to the skin.
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lichen simplex chronicus

An itching papular eruption that is circumscribed and located on skin that has become thickened and pigmented as a result of scratching. Synonym: circumscribed neurodermatitis See: neurodermatitis for illus.

lichen spinulosus

Keratosis pilaris.

lichen striatus

A papular eruption usually seen on one extremity of a child. It is arranged in linear groups and consists of pink papules. The disease, though self-limiting, may last for a year or longer.

tropical lichen

Prickly heat.

lichen tropicus

Prickly heat.
Medical Dictionary, © 2009 Farlex and Partners


Any skin eruption.
Collins Dictionary of Medicine © Robert M. Youngson 2004, 2005


a composite organism formed by the symbiotic association (see SYMBIOSIS of a green alga or a CYANOBACTERIUM and a fungus, usually from the ASCOMYCOTA or BASIDIOMYCOTA. The fungus makes up 80–90% of the association. The fungus gains oxygen and carbohydrates from the alga or cyanobacterium. The alga or cyanobacterium gains water, CO2 and mineral salts from the fungus and is protected from desiccation. Lichens reproduce vegetatively by means of soredia (hyphal cells enclosing algal or cyanobacterial cells) and sexually by means of the fungal apothecia or PERITHECIA. However, where no algae or cyanobacteria of the usual association occur, the germinating fungal spore dies. Lichens are very common on trees and rocks in unpolluted areas and can be used as an INDICATOR SPECIES.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005