Dermatological Skin Conditions

Our skin is the largest organ of the body and is exposed to a variety of external and internal factors that can lead to different skin conditions. Below are some common dermatological skin conditions, their descriptions, and brief explanations of their causes.

Basal cell carcinoma (BCC) is a prevalent type of skin cancer that arises from keratinocytes, often referred to as nonmelanoma skin cancer. It is the most common form of skin cancer and is sometimes called a rodent ulcer or basalioma. Individuals diagnosed with BCC frequently develop multiple primary tumors over the course of their lives.

The development of BCC is influenced by multiple factors:

The causes of cutaneous squamous cell carcinoma (SCC) are linked to various factors, including:

Melanoma, also known as malignant melanoma, is a potentially life-threatening form of skin cancer characterized by the uncontrolled growth of melanocytes, the pigment-producing cells in the skin. Normally, melanocytes are located in the basal layer of the epidermis, where they produce melanin, a pigment that protects skin cells by absorbing harmful ultraviolet (UV) radiation. While non-cancerous growths of melanocytes lead to moles (benign melanocytic nevi) and freckles (ephelides and lentigines), the malignant growth of these cells results in melanoma.

Melanoma is believed to originate from the uncontrolled growth of melanin-producing cells (melanocytic stem cells) that have undergone genetic changes. These mutations can be either acquired or inherited. Acquired or ‘sporadic’ mutations, which occur due to cell damage over a person’s lifetime, are the most common cause of melanoma. The primary culprit is overexposure to UV radiation from the sun or tanning beds.

Inherited (familial) melanoma, though far less common (under 10%), results from germline mutations passed down from parents. The CDKN2A gene (also known as p16INK4A or MTS1) is linked to 20-40% of familial melanomas. Other genes such as CDK4, MC1R, MITF, TERT, ACD, BAP1, POT1, and TERF2IP have also been implicated in recent years.

Cutaneous melanoma can develop on seemingly normal skin (in approximately 75% of cases) or from an existing mole or freckle that begins to grow larger and change in appearance.

Melanoma in situ is the earliest stage of melanoma, where cancerous cells are confined to the epidermis, the outermost layer of the skin. Also referred to as in-situ melanoma or level 1 melanoma, it has not yet spread to deeper layers. Since melanoma in situ poses no immediate threat to life, early detection is crucial for improving survival rates. Identifying melanoma at this early stage reduces the risk of complications, lowers treatment costs, and leads to better outcomes compared to more advanced stages of the disease.

Melanoma in situ is marked by genetic mutations in the DNA of melanocytes, primarily caused by exposure to ultraviolet (UV) radiation. These mutations trigger abnormal cell growth, leading to the early development of melanoma, although the cancerous cells remain confined to the epidermis at this stage.

The term “dysplastic nevus” specifically refers to a mole with distinct microscopic characteristics. However, only a small percentage of clinically atypical nevi meet the criteria for a dysplastic nevus upon microscopic examination. Many nevi that are histologically dysplastic may appear clinically normal, often being small, uniformly colored, and structurally consistent.

The causes of dysplastic nevi are primarily related to genetic and environmental factors:

Seborrheic keratosis is a benign, warty growth commonly seen in adults as a sign of skin aging. These lesions can vary in number, with some individuals developing hundreds over their lifetime. Also known as seborrheic keratosis (American spelling: seborrheic keratosis), it may be referred to as SK, basal cell papilloma, senile wart, brown wart, wisdom wart, or barnacle.

The broader term “benign keratosis” encompasses several related scaly skin lesions, including:

The exact cause of seborrheic keratoses is not well understood. Despite the name, these lesions are not confined to the seborrheic areas (such as the scalp, mid-face, chest, and upper back) associated with seborrheic dermatitis. They are not formed from sebaceous glands like sebaceous hyperplasia, nor are they related to sebum production, which is oily.

Seborrheic keratoses are considered degenerative in nature, meaning they tend to increase in number as individuals age. In some cases, a genetic predisposition can lead to the development of a large number of these lesions.

Actinic keratosis is a precancerous, scaly spot that appears on skin damaged by sun exposure, also known as solar keratosis. It is considered an early form of cutaneous squamous cell carcinoma (a type of keratinocyte cancer) and may potentially develop into skin cancer if left untreated.

Actinic keratoses develop due to abnormal skin cell changes resulting from DNA damage caused by short-wavelength UVB radiation. They are more likely to occur in individuals with compromised immune function, which can be due to aging, recent sun exposure, underlying health conditions, or the use of certain medications.

An intradermal nevus is a type of mole or birthmark that occurs within the dermis, the layer of skin located below the epidermis. Unlike other types of nevi, which may be located in the epidermis or at the junction between the epidermis and dermis, intradermal nevi are characterized by their placement entirely within the dermal layer.

Intradermal nevi are commonly seen in adults and are often removed for cosmetic reasons or if there is any concern about changes in appearance.

The exact cause of intradermal nevi is not fully understood, but several factors are believed to contribute to their development:

Overall, while these factors can influence the development of intradermal nevi, they are typically benign and not associated with cancer.

A dermatofibroma is a common benign fibrous nodule typically found on the skin of the lower legs. It is also known as a cutaneous fibrous histiocytoma. These nodules are usually firm, raised, and can vary in color from brown to reddish. They are composed of fibrous tissue and are generally harmless, although they can be removed for cosmetic reasons or if they cause discomfort.

The exact nature of dermatofibromas remains uncertain, with debate over whether they represent a reactive process or a true neoplasm. These lesions consist of proliferating fibroblasts, and histiocytes may also be involved. While dermatofibromas are sometimes linked to minor trauma, such as insect bites, injections, or injuries from rose thorns, this association is not consistent.

Additionally, multiple dermatofibromas can occur in individuals with altered immune systems, including those with HIV, immunosuppression, or autoimmune conditions.

Pilomatricoma is an uncommon, benign tumor that originates from hair matrix cells, which are involved in hair follicle development. Also spelled “pilomatrixoma,” it is sometimes referred to as “calcifying epithelioma of Malherbe.” Though harmless, pilomatricomas can present as firm, raised lumps under the skin and are typically found on the face, neck, or upper body.

The cause of pilomatricoma is attributed to a localized mutation in hair matrix cells. This mutation involves an overactive proto-oncogene called BCL-2, which indicates that the normal process of cell death is suppressed. In most cases, mutations in the CTNNB1 gene lead to the dysregulation of a protein complex known as beta-catenin/LEF-1, contributing to the formation of the tumor. These genetic changes disrupt normal cell processes, leading to the benign growth seen in pilomatricomas.

Lentigo simplex is the most common form of lentigo, characterized by a single or multiple lesions (lentigines) that may appear at birth or, more commonly, in early childhood. Unlike other types of lentigines, lentigo simplex is not triggered by sun exposure and is not linked to any underlying medical conditions. It is also known as simple lentigo or juvenile lentigo. These spots are generally harmless and benign.

The exact cause of lentigo simplex is unknown. When multiple lentigines appear without any associated medical conditions, the condition is termed lentigines profusa or generalized lentigines. However, when multiple lentigines are accompanied by other abnormalities, they become part of specific disease syndromes, such as:

Each of these syndromes involves distinct clinical features beyond the presence of lentigines.

A junctional nevus is a type of mole where the melanocytes (pigment-producing cells) are located at the junction between the epidermis (outer layer of skin) and the dermis (the layer just below). These nevi are usually flat or slightly raised and tend to be darker in color, ranging from brown to black.

Key features of junctional nevi:

In some cases, junctional nevi can evolve into compound or intradermal nevi over time.

The exact cause of a junctional nevus is not fully understood, but several factors may contribute to its development:

These moles are typically benign, but changes in size, shape, or color should be monitored, as they can occasionally indicate a risk of malignancy.

Key features of a compound nevus:

Compound nevi may evolve over time, with some eventually becoming intradermal nevi as melanocytes migrate deeper into the skin.

The exact causes of a compound nevus are not fully understood, but several factors are believed to contribute to its development:

While compound nevi are usually benign, changes in size, shape, or color may warrant further medical evaluation, as they could indicate an increased risk of melanoma.