The integumentary system, which includes your skin, hair, nails, and glands, is vulnerable to a wide range of diseases. These span from common bacterial infections and chronic inflammatory conditions to cancers, genetic disorders, and skin symptoms triggered by diseases elsewhere in the body. Some are minor annoyances; others are life-threatening. Here’s a practical breakdown of the major categories and the specific conditions within each.
Bacterial, Viral, and Fungal Infections
Infections are the most frequent diseases of the integumentary system, and they fall into three main groups based on the type of organism involved.
Bacterial skin infections are most commonly caused by Staphylococcus aureus and group A streptococci. These organisms are responsible for a range of conditions depending on how deep they penetrate. Impetigo is a superficial infection that produces crusty sores, typically on the face in children. Cellulitis is a deeper, more diffuse infection of the tissue beneath the skin, usually caused by streptococci, that produces spreading redness, warmth, and swelling. Folliculitis involves infected hair follicles and looks like small red bumps or whiteheads. When a follicle infection goes deeper and forms a painful, pus-filled lump, it becomes a furuncle, commonly known as a boil.
Herpes simplex is the most common viral skin disease. Type 1 typically causes cold sores around the mouth, while type 2 is associated with genital lesions. Human papillomaviruses cause warts, and poxviruses are responsible for molluscum contagiosum, a condition that produces small, firm, dome-shaped bumps on the skin.
Fungal infections frequently target both skin and nails. The fungus Trichophyton rubrum is the most prevalent cause of skin and nail fungal infections worldwide. Nail fungal infections (onychomycosis) can take several forms: the nail may thicken and turn yellow or white, become brittle, or develop a chalky surface. These infections are notoriously slow to clear because nails grow slowly and the fungus embeds itself beneath the nail plate.
Psoriasis and Eczema
These two chronic inflammatory conditions are among the most common non-infectious skin diseases. Both involve immune system dysfunction, skin barrier problems, genetic predisposition, and environmental triggers, but they work through different immune pathways and look quite different on the skin.
Atopic dermatitis (eczema) is driven primarily by a type of immune response associated with allergic reactions. This immune activity impairs the skin’s ability to produce key barrier proteins, making the skin more permeable to irritants, allergens, and bacteria. The result is dry, intensely itchy patches that can crack and weep, most often appearing in the creases of elbows, behind knees, and on the face. Because the skin barrier is compromised, people with eczema are also more prone to skin infections.
Psoriasis works differently. It typically starts when something damages the outer skin layer, whether physical trauma, an infection, or certain medications. Damaged skin cells release signals that activate a different branch of the immune system, triggering rapid overproduction of new skin cells. The result is thick, raised, red or silvery-scaled plaques that commonly appear on the elbows, knees, scalp, and lower back. Psoriasis involves chronic, system-wide inflammation, meaning it can also affect the joints and increase cardiovascular risk over time.
Skin Cancer
Three main types of cancer originate in the skin, each arising from a different cell type in the epidermis.
Basal cell carcinoma forms in the basal cells at the bottom of the epidermis. It’s the most common form of skin cancer and typically appears as a pearly or waxy bump, often on sun-exposed areas like the face, ears, or neck. It grows slowly and rarely spreads to other parts of the body, but it can cause significant local tissue damage if left untreated.
Squamous cell carcinoma develops in the flat cells that make up the outer surface of the skin. It often looks like a rough, scaly lesion or a sore that crusts, bleeds, and won’t fully heal. This type is more likely than basal cell carcinoma to spread, particularly if it develops on the lips, ears, or in areas of chronic scarring.
Melanoma is the least common but most dangerous form. It arises from melanocytes, the cells that produce skin pigment. The overall five-year survival rate for melanoma is about 95%, but that number depends heavily on when it’s caught. When melanoma is still localized to the original site, which accounts for 77% of diagnoses, the five-year survival rate is essentially 100%. Once it spreads to distant parts of the body, that number drops to about 35%. The ABCDE rule helps identify suspicious moles: look for asymmetry, irregular borders, multiple colors, a diameter larger than a pencil eraser (6 mm), and any evolution in size, shape, or color. Evolution is considered the most important sign.
Diseases of Hair and Nails
The integumentary system includes hair follicles and nails, and several diseases specifically target these structures.
Alopecia areata is a common form of non-scarring hair loss in which the immune system attacks hair follicles, causing patches of hair to fall out. In some cases, it progresses to total scalp hair loss (alopecia totalis) or loss of all body hair (alopecia universalis). It also frequently affects the nails, causing pitting, rough or opaque nails (trachyonychia), white spots, and brittle texture. Alopecia areata sometimes runs in families.
Lichen planus is another inflammatory condition that can affect skin, hair, and nails simultaneously. When it targets nails, it can produce changes very similar to those seen in alopecia areata, sometimes requiring a biopsy to tell the two apart. Psoriasis and eczema can also cause nail changes, including pitting, ridging, and separation of the nail from the nail bed.
Glandular Conditions
Your skin contains millions of sebaceous (oil) glands and sweat glands, and both can become diseased.
Acne vulgaris is the most familiar example. It develops when sebaceous glands produce excess oil, which combines with dead skin cells to clog hair follicles. Bacteria multiply in the blocked pore, triggering inflammation that produces the whiteheads, blackheads, and deeper cysts most people associate with acne.
Hidradenitis suppurativa, sometimes called acne inversa, is a more severe chronic condition caused by blockages in hair follicles in areas where skin rubs together, particularly the armpits, groin, and under the breasts. Trapped bacteria cause deep, painful, boil-like lumps that can rupture and drain pus. Over time, repeated flare-ups lead to tunnels under the skin and significant scarring. It typically begins after puberty, usually in the teens or twenties, and genetics, hormones, and environmental factors all play a role.
Genetic Skin Disorders
Some integumentary diseases are caused by inherited gene mutations that disrupt the skin’s normal growth cycle.
Ichthyosis is a group of more than 30 distinct genetic conditions that cause dry, thickened, scaly skin. In all forms, mutated genes cause skin cells to either grow faster than they can be shed or fail to separate from the skin surface properly. Ichthyosis vulgaris, the most common and mildest type, typically appears in the first year of life as persistent dry, flaky skin. More severe forms include lamellar ichthyosis, where infants are born encased in a tight, clear membrane that peels away over weeks to reveal large, dark, plate-like scales across most of the body. Harlequin ichthyosis is the most severe form, present at birth with thick plates of skin that can restrict joint movement and alter facial features. X-linked ichthyosis affects mostly males, beginning around 3 to 6 months of age, and tends to worsen over time.
Albinism is another genetic condition affecting the integumentary system. It results from mutations that reduce or eliminate melanin production, leaving the skin, hair, and eyes with little to no pigment. Beyond its cosmetic effects, the lack of melanin dramatically increases vulnerability to UV damage and skin cancer.
Skin Signs of Systemic Disease
Sometimes skin symptoms are the visible surface of a disease affecting the entire body. Recognizing these signs can lead to earlier diagnosis of the underlying condition.
Systemic lupus erythematosus is the classic example. Its hallmark skin feature is the malar, or butterfly, rash: a flat or slightly raised redness that stretches across both cheeks and the bridge of the nose, typically sparing the creases beside the nostrils. This rash has a specificity of 96% for lupus, meaning it very rarely appears in other conditions. Lupus can also cause deeper skin involvement called lupus profundus, where firm nodules form under the skin and can leave depressed scars as they heal.
Scleroderma causes progressive hardening and tightening of the skin due to excessive collagen production. It often starts in the fingers and can spread to the face and trunk, limiting movement and changing facial appearance. Diabetes frequently manifests in the skin as well, producing slow-healing wounds, darkened patches of skin in body folds, and increased susceptibility to bacterial and fungal infections.
How Skin Diseases Are Diagnosed
Most skin conditions start with a visual examination, but several tools help confirm a diagnosis when the cause isn’t immediately clear. Dermoscopy uses a handheld magnifying device with polarized light to examine skin structures invisible to the naked eye. It increases the accuracy of skin cancer detection compared to looking at a lesion unaided, allows doctors to identify thinner (earlier) melanomas, and reduces unnecessary biopsies by helping distinguish harmless growths from potentially dangerous ones.
When dermoscopy reveals concerning features, such as an irregular or disorganized pattern, blue-black or gray coloring, or the presence of ulceration, a biopsy is the next step. This involves removing a small sample of tissue for examination under a microscope. For suspected allergic skin conditions, patch testing can identify specific substances triggering a reaction by applying small amounts of common allergens to the skin and monitoring the response over 48 to 72 hours.