Principles of dermatology

Last updated: July 14, 2022

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Dermatology is the branch of medicine concerned with the skin, hair, and nails as well as the conditions associated with them. Basic knowledge of dermatology is essential for every physician, as approximately 50% of skin-related consultations are initially assessed by non-dermatologists. In the United States, the most common conditions seen by dermatologists include acne, actinic keratoses, non-melanoma skin cancers, benign tumors, and contact dermatitis. Skin lesions may be primary or secondary. Primary lesions (e.g., macules and papules) appear as a direct result of a disease process. Secondary lesions (e.g., scales and ulcers) may develop from primary lesions or result from external trauma (e.g., infections, scratching). Dermatological conditions can often be diagnosed based on patient history and physical examination but confirming the diagnosis may require laboratory testing or biopsy. Dermatological diseases are managed with medication (topical and systemic) and procedures such as surgery, cryoablation, radiotherapy, or phototherapy. Conservative treatment with topical agents is the treatment of choice for most dermatological conditions, with systemic medication and/or surgery being employed only if necessary. The prevalence, manifestations, and treatment of dermatological conditions in skin of color may vary depending on skin tone and genetic inheritance.

  • Complete skin assessment: Examine the skin (including the hands, mouth, and scalp) and nails for signs of dermatological conditions.
  • Examination techniques
    • Inspection
    • Palpation: evaluation of consistency (e.g., softness, firmness)
    • Typical skin tests, as indicated:
    • Dermatoscope inspection, as indicated
  • Confirmation of diagnosis: may require biopsy for histopathological examination (see “Dermapathology” below) and/or laboratory studies

The hands, mouth, scalp, and nails should not be overlooked during a dermatological examination.

Skin examination

  • Determine the type of lesion: See primary skin lesions, secondary skin lesions, and complex skin lesions below.
  • Record lesion characteristics
    • Location
    • Number (single/multiple)
    • Size
    • Color: e.g., pink discoloration
    • Texture: e.g., atrophic, calloused, crusty, verrucous
    • Shape: e.g., round, oval, annular
    • Distribution
      • Symmetric/asymmetric
      • Unilateral/bilateral
      • Diffuse/grouped
    • Secondary changes (e.g., as a result of scratching)

Physical examination

Nail examination

Alterations of the nails
Clinical findings Clinical examples Possible underlying disease

Nail pitting


Nail clubbing

Koilonychia (spoon nails)

White, grey, or yellowish color with dullness and crumbling of the nail

Mees lines (horizontal lines of discoloration)

Examination of the hands

Alterations of the hands
Clinical findings Clinical examples Possible underlying disease
  • -
  • -
Overview of most common primary skin lesions [1][2]
Primary Lesions Description Cross-section Clinical example


Patch (dermatology)

Nodule (dermatology)
  • An elevated lesion, > 1 cm in both diameter and depth
Plaque (dermatology)
Vesicle (dermatology)
Overview of most common secondary skin lesions [1][2]
Secondary Lesions Description Illustration Clinical example
Scale (dermatology)
Fissure (cleft)
Ulcer (dermatology)
  • Rounded or irregularly shaped deeper lesions that result from loss of the epidermis and some portion of the dermis.
Excoriation (scratch marks)
  • Abrasion produced by mechanical force, usually involving the epidermis (but may reach the outer layer of the dermis)
Skin atrophy
  • Composed of new connective tissue that has replaced lost substance
  • An overgrowth of scar tissue manifests as a keloid (thickened, raised tissue that grows beyond the borders of the scar and shows no regression).
Overview of complex skin lesions [3]
Complex lesions Description Clinical example



  • Caused by bleeding into subcutaneous tissue, muscle, organ tissue or a cavity
    • Immediately after trauma: red
    • After 24–96 h: dark red, green, blue, purple, black
      • Cause: coagulation of the blood and degradation of hemoglobin into bile pigment
    • After 4–7 days: dark green
    • After 7 days: yellow; brownish
Purpura (a subtype of hematoma that does not blanch upon the application of pressure) Nonpalpable purpura


  • Flat, red-purple, pinpoint lesions < 3 mm in size

  • Flat, red-purple, larger form of petechiae, > 5 mm in size
Palpable purpura
  • Raised, red-purple lesions
Rashes Exanthem
  • Extended uniform rash (localized or generalized)
  • Reddening of the skin as a result of vasodilation (blanches if pressure is applied)
  • Generalized reddening of the skin
Maculopapular rash
Further lesions Lichenification
  • Thickening of the skin with accentuated skin markings
Histopathologic finding Characteristics Examples of associated conditions


  • Topical medications
    • First choice of treatment for most conditions; often preferred for treating dermatological conditions because they cause fewer systemic side effects
    • Examples: antibiotics, antifungals, corticosteroids, cytotoxic agents, antipruritics, retinoids
  • Systemic medications
  • Procedures
    • Surgery
    • Cryoablation: application of cold (e.g., using liquid nitrogen) to destroy abnormal tissue, malignant or premalignant skin lesions.
  • Other

Types of topical preparations [5]

  • Creams
  • Ointments
  • Lotions, foams, and gels

Topical steroids

Topical steroids are the most frequently used topical treatment in dermatology.

Agent Potency Indication
Hydrocortisone (1%) Low For mild and chronic dermatoses and for use on the face
Triamcinolone (0.1%) Medium For intermediate severity dermatoses
Clobetasol (0.05%) High For more severe dermatoses


  • Skin of color” refers to skin with a higher degree of pigmentation than that traditionally associated with Northern European heritage.
    • Skin tone is a spectrum that does not necessarily correspond to the skin tones traditionally associated with race.
    • Genetic inheritance can play a more important role in the manifestation of dermatological conditions than skin tone.
    • It is important to recognize with regard to the concept of “race” still in use by the US Census Bureau that there is no foundation for a scientific concept of race as a specific genetic, phenotypical, ancestral, or ethnic trait that distinguishes all members of one population from those of another.
  • Western medicine has traditionally focused on the presentation of light-skinned individuals, leading to underrepresentation in dermatological resources of cutaneous manifestations in individuals with skin of color.
  • Changing demographics and increased representation of historically marginalized populations have raised awareness for the need and importance of thoroughly understanding skin of color.


  • The incidence and prevalence of dermatological conditions in individuals with skin of color depend to a high degree on skin tone and differ from those seen in light-skinned individuals for a variety of reasons:
    • Underrecognition due to poor dermatological training in diagnosing cutaneous conditions in individuals with skin of color.
    • Factors that are influenced by different lifestyle and cultural practices
    • Genetic inheritance
Dermatological conditions that are more common in individuals with skin of color [9][10][11]
Heritage Condition(s) with higher prevalence
Southeast Asian
East Asian
West Asian
Latin American
American Indian

Physiology [20][21]

Skin color depends on the degree of pigmentation with melanin (contained in melanosomes, which are synthesized in melanocytes), other pigments (i.e., hemoglobin, oxyhemoglobin, and carotenoids), and melanocyte activity, all of which are determined by genetic heritage. For more information on melanin, see “Cells of the skin” in “Skin and skin appendage.”

  • Differences in skin pigmentation are mainly due to differences in melanocytic activity.
  • Skin layer composition varies between different skin colors.
    • Stratum corneum (SC)
      • The darker the skin, the more keratinocyte cell layers and greater intercellular cohesion it will have.
      • Thickness: similar in all skin colors
      • Lipid content: is highest in individuals with Southeast and East Asian heritage, followed by those with Hispanic and African heritage
      • Barrier function (greater transepidermal fluid loss): African heritage > Hispanic heritage > Southeast and East Asian heritage
    • The greater the amount and size of fibroblasts, small collagen fibers, and macrophages, the higher the risk of keloid formation and scarring
  • Skin appendages: larger sebaceous glands → increased sebum production (African heritage > Southeast and East Asian heritage > Hispanic heritage)

Clinical presentation [22]

  • Dermatological symptoms may be subtle or have a characteristic appearance depending on skin pigmentation.
Overview of dermatological symptoms in skin of color
Symptom Description Clinical example(s)
  • May appear gray-brown against a background with darker pigmentation or may only be apparent in certain areas less exposed to sunlight or with lighter pigmentation (e.g., palmar surfaces or mucous membranes).
  • May appear purple or brown rather than pink or red when against a background with darker pigmentation
  • May be more readily apparent against a background with darker pigmentation
  • May appear as a grayish or lighter color in some patients or may only be apparent in areas less exposed to sunlight or with lighter pigmentation (e.g., palmar surfaces, mucous membranes, and nailbeds)
Skin hemorrhages
  • May appear dark purple, brown, or even black against a background of darker pigmentation
  • Early bruising may not be visible at all
  • Specific conditions may appear uniquely in individuals with skin of color [23]
Distinguishing features of specific conditions in individuals with skin of color [23]
Condition Description Clinical example
Atopic dermatitis
  • May have more papular or follicular accentuation
Basal cell carcinoma
  • More commonly pigmented with a black or pearly brown appearance
Acne vulgaris

Diagnostic considerations

  • The prevalence, manifestations, and treatment of dermatological conditions may vary depending on skin tone and genetic inheritance.
  • Lack of familiarity with the manifestations of dermatological conditions in individuals with skin of color may lead to a delay or failure to properly recognize, diagnose, and treat dermatological conditions in these patient groups.
  • Keep the following recommendations in mind regarding patients with skin of color to ensure proper diagnosis and treatment:
    • Appreciate the diversity of skin tones and consider the characteristics of every patient's skin individually.
    • Familiarize yourself with differences in disease manifestations, epidemiology, and treatment of dermatological conditions that depend on skin color.
    • Familiarize yourself with and be sensitive to differences that depend on skin color and/or ethnicity in skincare (e.g., dandruff products), cosmetic use (e.g., skin bleaching products), and cultural practices (e.g., tattooing, hair extensions).
    • Familiarize yourself with the preferred terms for describing skin tones and those that should be avoided.
    • Raise awareness for common misconceptions regarding skin of color (e.g., that people of color do not require sunscreen, do not get sunburnt, and do not get skin cancer).
    • Perform a complete skin assessment upon initial presentation and familiarize yourself with the patient's normal skin tone to better recognize irregularities and lesions.
    • Use a patient-centered approach and be open about pertinent gaps in knowledge, involving the patient in helping to close them.
    • Be aware of the history of racism and its consequences also in health care, but refrain from making assumptions (e.g., regarding social status) based on skin color (see also “Social aspects of health care”).

Treatment considerations [22]

  1. Freeman et al.. Corns and Calluses Resulting from Mechanical Hyperkeratosis. American Family Physician. 2002 .
  2. Description of Skin Lesions. Updated: June 1, 2016. Accessed: May 15, 2017.
  3. Primary Care Dermatology Module, Nomenclature of Skin Lesions. Updated: May 15, 2017. Accessed: May 15, 2017.
  4. Leung AK, Chan KW. Evaluating the child with purpura. Am Fam Physician. 2001; 64 (3): p.419-428.
  5. Principles of Topical Dermatologic Therapy. Updated: March 1, 2017. Accessed: September 3, 2017.
  6. Alexis AF, Barbosa VH. Skin of Color. Springer Science & Business Media ; 2012 : p. XIV, 382
  7. Silverberg NB, Durán-McKinster C, Tay Y-K. Pediatric Skin of Color. Springer ; 2015 : p. XV, 473
  8. Kelly AP, Serrano AM, Taylor S, Lim H. Taylor and Kelly's Dermatology for Skin of Color. McGraw-Hill Education / Medical ; 2016
  9. Kundu RV, Patterson S. Dermatologic conditions in skin of color: part I. Special considerations for common skin disorders.. Am Fam Physician. 2013; 87 (12): p.850-6.
  10. Kundu RV, Patterson S. Dermatologic conditions in skin of color: part II. Disorders occurring predominately in skin of color.. Am Fam Physician. 2013; 87 (12): p.859-65.
  11. Ho SGY, Chan HHL. The Asian Dermatologic Patient. Am J Clin Dermatol. 2009; 10 (3): p.153-168. doi: 10.2165/00128071-200910030-00002 . | Open in Read by QxMD
  12. Glass DA. Current Understanding of the Genetic Causes of Keloid Formation. Journal of Investigative Dermatology Symposium Proceedings. 2017; 18 (2): p.S50-S53. doi: 10.1016/j.jisp.2016.10.024 . | Open in Read by QxMD
  13. Hena KM. Sarcoidosis Epidemiology: Race Matters. Frontiers in Immunology. 2020; 11 . doi: 10.3389/fimmu.2020.537382 . | Open in Read by QxMD
  14. Dumas O, Abramovitz L, Wiley AS, Cozier YC, Camargo CA Jr. Epidemiology of Sarcoidosis in a Prospective Cohort Study of U.S. Women.. Annals of the American Thoracic Society. 2016; 13 (1): p.67-71. doi: 10.1513/AnnalsATS.201508-568BC . | Open in Read by QxMD
  15. Ogunbiyi A. Acne keloidalis nuchae: prevalence, impact, and management challenges. Clinical, Cosmetic and Investigational Dermatology. 2016; Volume 9 : p.483-489. doi: 10.2147/ccid.s99225 . | Open in Read by QxMD
  16. Price KN, Hsiao JL, Shi VY. Race and Ethnicity Gaps in Global Hidradenitis Suppurativa Clinical Trials. Dermatology. 2019; 237 (1): p.97-102. doi: 10.1159/000504911 . | Open in Read by QxMD
  17. Davatchi F, Chams-Davatchi C, Shams H, et al. Behcet’s disease: epidemiology, clinical manifestations, and diagnosis. Expert Review of Clinical Immunology. 2016; 13 (1): p.57-65. doi: 10.1080/1744666x.2016.1205486 . | Open in Read by QxMD
  18. Handel AC, Miot LDB, Miot HA. Melasma: a clinical and epidemiological review. An Bras Dermatol. 2014; 89 (5): p.771-782. doi: 10.1590/abd1806-4841.20143063 . | Open in Read by QxMD
  19. Toussaint-Caire S. Actinic Prurigo. Springer New York ; 2015 : p. 387-395
  20. Taylor SC. Skin of color: Biology, structure, function, and implications for dermatologic disease. J Am Acad Dermatol. 2002; 46 (2): p.S41-S62. doi: 10.1067/mjd.2002.120790 . | Open in Read by QxMD
  21. Naik PP, Farrukh SN. Influence of ethnicities and skin color variations in different populations- A Review. Skin Pharmacol Physiol. 2021 . doi: 10.1159/000518826 . | Open in Read by QxMD
  22. Taylor SC, Gathers RC, Callender VD, Rodriguez DA, Badreshia-Bansal S. Treatments for Skin of Color E-Book. Elsevier Health Sciences ; 2011
  23. Gupta AK, Bharadwaj M, Mehrotra R. Skin Cancer Concerns in People of Color: Risk Factors and Prevention. Asian Pac J Cancer Prev. 2016; 17 (12): p.5257-5264. doi: 10.22034/APJCP.2016.17.12.5257 . | Open in Read by QxMD
  24. Marks JG Jr, Miller JJ . Lookingbill and Marks' Principles of Dermatology. Saunders Elsevier ; 2013
  25. Amirlak B. Skin Anatomy. In: Caputy GG, Skin Anatomy. New York, NY: WebMD. Updated: July 18, 2015. Accessed: May 15, 2017.
  26. Structure of Normal Skin. Updated: May 15, 2017. Accessed: May 15, 2017.
  27. Layers of the Skin. Updated: May 15, 2017. Accessed: May 15, 2017.
  28. Zhang S-X. An Atlas of Histology. Springer Science & Business Media ; 2013

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