Skin Diseases HealthQM

What Are the Most Common Skin Diseases?

Skin diseases are associated with conditions that affect the structure or function of the skin, causing irritation, clogging, or damage. Although there are many skin diseases, the following are the most common:

  • Acne
  • Atopic Dermatitis
  • Hair Loss
  • Psoriasis
  • Rosacea
  • Skin Cancers

Acne is the most common skin condition in the United States and affects up to 50 million Americans annually, while 1 in 10 individuals will develop atopic dermatitis during their lifetime [1].

Hair loss affects about 80 million Americans including 50 million men and 30 million women, while psoriasis affects about 7.5 million Americans.

Rosacea affects 16 million Americans, while skin cancer affects 9500 individuals a day in the United States [1].

1. What is Human Skin?

The skin is the external covering of our body and is made of 3 layers known as the epidermis, the dermis, and the hypodermis [2].

1.1. What Is Epidermis and Its Function?

The epidermal layer or epidermis is the outer waterproof layer of the skin and is involved in protecting the body from pathogens found in the environment.

The epidermis is made of 5 layers which are (from inside out): stratum basale, stratum spinosum, stratum granulosum, stratum lucidum, and stratum corneum.

The epidermis contains several types of cells including keratinocytes, melanocytes, Langerhans’ cells, and Merkle’s cells.

  • What Is the Role of Keratinocytes?

Keratinocytes are produced by the stratum basale (basal layer) and are involved in the production of keratin that provides the waterproof function of the epidermis.

Keratinocytes are also involved in transforming cholesterol precursors into vitamin D through ultraviolet light B (UVB).

  • What Is the Role of Melanocytes?

Melanocytes are cells that produce melanin (skin pigment) and are found within the stratum basale of the epidermis.

  • What Are Langerhans’ cells?

Langerhans’ cells are immune cells (dendritic cells) that collect information about pathogens (antigens) to inform the immune system. They are found in the stratum spinosum.

  • What Are Merkle’s cells?

Merkel’s cells or Disks are receptors found in the stratum basale of the epidermis of non-hairy skin (e.g., fingertips) and are involved in touch through their capacity to sense corners, curves, and edges.

1.2. What Is Dermis and Its Function?

The dermis sits just below the stratum basale of the epidermis. It is composed of two layers of conjunctive tissue (supportive tissues): the papillary layer and the reticular layer.

Although both layers are supportive types of tissue, the reticular layer also contains collagen, hair follicles, hair, sweat glands, blood vessels, sensory neurons, and muscles.

1.3. What Is Hypodermis and Its Function?

The hypodermis is the deepest layer of the skin and contains adipose (fat) lobules, blood vessels, and sensory neurons.

2- What Are the 6 Functions of the Skin?

The skin has many functions, and the following are some of the most important:

  • Protection against pathogens found on the surface of the skin through the involvement of Langerhans’ cells and perspiration that breaks down some pathogens.
  • The skin contains thermoreceptors that contribute to the regulation of body temperature.
  • The skin keratinocytes help transform cholesterol precursors into vitamin D through ultraviolet light B (UVB).
  • The skin prevents excessive evaporation of water.
  • Some of the metabolic waste such as urea is eliminated through the skin.
  • The skin is the waterproof layer of the body.

3- Most Common Skin Diseases

3.1. Acne

Acne is the clogging of the hair follicle by dead skin and oil produced by the sebaceous glands of the skin known as sebum.

Acne is mainly seen in teenagers but also individuals of all ages.

3.1.1. What Causes Acne?

Acne can be due to the following factors:

  • Excessive production of sebum which may be due to hormonal changes during puberty or pregnancy.
  • Bacterial infection such as by Cutibacterium acnes.
  • Inflammation.

3.1.1. What Are the Symptoms of Acne?

Acne is characterized by the following symptoms that appear on the face, forehead, shoulders, chest, and upper back:

  • Whiteheads or blackheads
  • Red bumps
  • Painful lumps under the skin
  • Pus filled lumps

3.2. Atopic Dermatitis

Atopic dermatitis or atopic eczema is a non-infectious chronic inflammation of the skin and the most common type of eczema.

3.2.1. What Are the Causes of Atopic Dermatitis?

The causes of atopic dermatitis are unknown; however, genetics, immune, and environmental factors (e.g., smoking, type of soap, or air pollutants) might be involved [3].

3.2.1. What Are the Symptoms of Atopic Dermatitis?

The skin symptoms include:

  • Itchiness
  • Redness
  • Swelling
  • Cracked skin
  • Crusting of the skin

3.3. Hair Loss

Hair loss, also known as alopecia or baldness is a temporary or permanent loss of hair that mainly affects men but is also observed in women.

3.2.1. What Are the Causes of Hair Loss?

Hair is associated with disorders that affect the scalp or the entire body such as illness, stress, iron deficiency, genetics, weight loss, aging, cancer treatment, and lifestyle.

  • Illnesses such as telogen effluvium, autoimmune diseases (e.g., alopecia areata), fungal infection (Tinea capitis), thyroid disorders (hyperthyroidism and hypothyroidism), sex hormone imbalance (Androgen sex hormone).
  • Acute and chronic Stress trigger stress hormones that affect the hair follicles.
  • Sudden weight loss.
  • Iron deficiency that affects the division of hair follicles.
  • Genetics associated with genetic variability of the androgen receptor (AR) gene.
  • Cancer treatment (chemotherapy).

3.4. Psoriasis

Psoriasis is an autoimmune disease characterized by increased and excessive production of the skin epidermis due to premature maturation of keratinocytes [4].

This premature maturation of keratinocytes is due to the overactivity of immune cells (Lymphocytes T).

3.4.1. What Are the Causes of Psoriasis?

Although immune cells (lymphocytes T) are responsible for psoriasis, the causes triggering the overactivity of the immune cells are not well known; however, some factors have been proposed:

  • Genetics
  • Stress and Anxiety
  • Skin Injury
  • Hormonal Changes
  • Infections (e.g., HIV, Staphylococcus aureus, and Candida albicans)
  • Medications (e.g., beta blockers, non-steroidal anti-inflammatory drugs, and lipid-lowering medications).

3.4.1. What Are the Symptoms of Psoriasis?

Psoriasis mostly affects the scalp, the back, the elbows, and the knees, and manifests with the following symptoms:

  • Plaques of red skin with silvery-white scales
  • Cracked skin with Itching or bleeding
  • Ridged and pitted nails

3.5. Rosacea

Rosacea is a chronic skin condition that mainly affects the face of individuals with fair skin. The causes are unknown; however, there are factors that trigger Rosacea:

3.5.1. What Are the Symptoms of Rosacea?

Rosacea manifests with the following symptoms:

  • Redness on cheek, nose, forehead, and chin
  • Tiny broken blood vessels
  • Small pink or red bumps
  • Swelling around the eyes

3.6. Skin Cancer

Skin cancers are cancers that develop from abnormal cells within the skin. There are 3 types of skin cancers: melanoma, squamous cell skin cancer, and basal cell skin cancer.

3.6.1. Melanoma

Melanoma is cancer that develops from the abnormal growth of melanin-producing cells known as melanocytes [5].

What Causes Melanoma?

  • Melanoma is caused by UV lights of the sun which cause damage to the DNA of melanocytes resulting in their transformation into cancer cells.
  • It can also be caused by inherited mutations in tumor suppressor genes.

What Are the Symptoms of Melanoma?

Early signs of melanoma may manifest with the following symptoms:

  • Changes in the shape or color of existing moles
  • Lumps on the skin
  • Itching, ulcerated, or bleeding moles.

Melanoma can become metastatic (spread) and affects other organs such as the brain, the liver, bones, and lymph nodes.

3.6.2. Squamous cell skin cancer

Squamous cell skin cancer is cancer that develops from the keratinocytes in the epidermis.

What Causes Squamous cell skin cancer?

  • Squamous cell skin cancer is caused by UV lights of the sun which cause damage to the DNA of keratinocytes resulting in their transformation into cancer cells.
  • Chronic Immunosuppressive medications [6].

What Are the Symptoms of Squamous cell skin cancer?

Squamous cell skin cancer may manifest with the following symptoms:

  • Red nodule on the scalp, lips, back of the hands, or ears.
  • Sporadic bleeding of the nodule, particularly on the lip.
  • Ulceration of the nodule with high raised edges

3.6.3. Basal cell skin cancer

Basal cell skin cancer is the most common type of skin cancer that develops from cells within the hair follicle known as trichoblasts [7].

What Causes Basal cell skin cancer?

  • UV lights of the sun are risks factors for Basal cell skin cancer.
  • Environmental factors such as ionizing radiations, immunosuppression, or arsenic ingestion.
  • Genetic factors

What Are the Symptoms of Basal cell skin cancer?

  • Shiny and pearly skin nodule
  • Red patch


Although there are factors, such as genetics, that cannot be controlled, lifestyles changes that protect our skin can certainly be applied in our everyday life as there are many skin diseases that are caused by environmental factors such as exposure to the sun (tanning), stress, or smoking.

Similar Posts