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Common Skin
Conditions

Explore the anatomy and physiology behind burns, acne, and dermatitis: how they disrupt skin structure, the body's repair mechanisms, and clinical classification.

Anatomy & Physiology

The Skin: Your Body's Largest Organ

The integumentary system accounts for roughly 16% of total body weight and covers approximately 1.5 to 2 square meters in the average adult. It serves as the first line of defense against pathogens, UV radiation, and mechanical trauma.

Protection
Physical barrier against microbes, chemicals, and UV light
Thermoregulation
Sweat glands and blood vessel dilation control body temperature
Sensation
Receptors detect touch, pressure, pain, and temperature changes

Three Layers of Skin Structure

Epidermis Keratinocytes, melanocytes, Langerhans cells Dermis Collagen, elastin, blood vessels, hair follicles, sebaceous glands, nerves Hypodermis (Subcutaneous) Adipose tissue, larger blood vessels Superficial Deep

Defining Burns, Acne, and Dermatitis

Burns
Tissue damage caused by heat, chemicals, electricity, or radiation that denatures proteins and destroys cells at varying depths.
Acne
Chronic inflammatory condition of pilosebaceous units involving excess sebum, clogged follicles, and bacterial colonization.
Dermatitis
Broad term for epidermal inflammation triggered by allergens, irritants, or immune dysfunction, causing redness and itching.

Burn Classification by Depth

Epidermis Dermis Hypodermis 1st Degree 2nd Degree 3rd Degree Superficial Epidermis only Partial thickness Epidermis + Dermis Full thickness All three layers

The Rule of Nines

The Rule of Nines estimates the total body surface area (TBSA) affected by burns. Each major body region is assigned a percentage that is a multiple of nine:

9% Front 18% Back: 18% 9% 9% 18% 18% Perineum: 1% Each arm Each leg: 18%

Key Distinction: Types of Burns

Feature Thermal Chemical Electrical
Cause Flames, hot liquids, steam Acids, alkalis, solvents Current passing through tissue
Damage pattern Superficial to deep at contact site Progressive: continues until neutralized Deep internal damage, exit wounds
Pain level High (1st/2nd), absent (3rd) Intense, worsening Variable, cardiac risk
First response Cool water, do not ice Flush with large volumes of water Ensure electrical source is off

Acne Pathophysiology

Excess Sebum Androgens Follicular Occlusion Hyperkeratinization Bacterial Colonization C. acnes Inflammation Immune response triggers redness and swelling Lesion Types: Comedones (blackheads/whiteheads) Papules & Pustules (inflamed, pus-filled) Nodules & Cysts (deep, severe)

Factors that Influence Acne

1
Hormonal changes: Androgens (especially testosterone) stimulate sebaceous glands, increasing sebum output during puberty, menstruation, and stress.
2
Bacterial colonization: Cutibacterium acnes thrives in anaerobic, lipid-rich environments created by clogged pores.
3
Hyperkeratinization: Excess keratin production traps dead skin cells inside the follicle, forming a plug (comedone).
4
Inflammation cascade: The immune system responds to bacterial byproducts, releasing cytokines that cause redness, swelling, and pain.

Types of Dermatitis

Contact Dermatitis
Caused by direct contact with an irritant (soap, solvents) or allergen (poison ivy, nickel). Localized rash at the contact site.
Atopic Dermatitis
Chronic eczema linked to genetic predisposition and immune dysfunction. Often appears in childhood with dry, itchy patches.
Seborrheic Dermatitis
Affects oil-rich areas (scalp, face, chest). Linked to yeast (Malassezia) overgrowth. Causes flaky, scaly patches.

How Contact Dermatitis Develops

1
Sensitization phase: First exposure to an allergen (e.g., urushiol in poison ivy). Langerhans cells present the antigen to T-cells. No visible reaction yet.
2
Memory formation: T-cells create immunological memory of the allergen. This process takes 10 to 14 days after first exposure.
3
Elicitation phase: Upon re-exposure, memory T-cells rapidly activate, releasing cytokines. This triggers erythema, edema, and vesicles within 24 to 72 hours.
4
Resolution: Once the allergen is removed, the immune response subsides over 1 to 3 weeks. Barrier repair follows via keratinocyte proliferation.

How to Classify a Skin Condition

1
Identify the trigger: Was there heat exposure (burn), hormonal/bacterial involvement (acne), or contact with an irritant/allergen (dermatitis)?
2
Assess the depth: Is damage limited to the epidermis, does it extend into the dermis, or does it reach the hypodermis?
3
Note the lesion morphology: Blisters (vesicles) suggest 2nd degree burns or contact dermatitis. Comedones indicate acne. Erythema alone may be 1st degree burn or irritant dermatitis.
4
Evaluate chronicity: Acute onset (burn) vs. chronic/recurring (atopic dermatitis, acne vulgaris).
5
Determine severity: Use classification systems: burn degree, acne grading (mild/moderate/severe), or dermatitis scoring (SCORAD).

Example 1: Classifying a Burn

Scenario: A patient spills boiling water on their forearm. The affected area shows intense redness, swelling, and large fluid-filled blisters. The patient reports severe pain at the site.

Epidermis: Damaged Dermis: Partially Damaged Nerve endings intact (pain present) Hypodermis: Intact blister blister

Example 2: Identifying Acne Severity

Scenario: A 16-year-old presents with blackheads and whiteheads on the forehead and nose, along with several red, raised bumps on the cheeks. No deep, painful nodules are observed.

Comedones
Blackheads (open comedones) and whiteheads (closed comedones) on the T-zone indicate follicular occlusion.
Papules
Red, raised bumps on cheeks confirm inflammatory response to trapped bacteria: immune cells infiltrate the follicle wall.

Example 3: Diagnosing Dermatitis

Scenario: A patient develops an intensely itchy, red rash with small vesicles on their wrist, exactly where they wear a new metal watch. The rash appeared 48 hours after wearing the watch and is sharply demarcated to the contact area.

1
Trigger identified: Nickel in the metal watch: a common allergen.
2
Timing: 48-hour delay is consistent with a Type IV hypersensitivity (delayed-type) reaction.
3
Morphology: Sharply demarcated, vesicular rash at the contact site confirms localized allergic response.
4
Depth: Epidermis only: no deep tissue damage.

Common Mistakes

✕ Confusing Burn Degrees
Students often think 3rd degree burns are the most painful. In fact, nerve destruction means the patient feels no pain at the burn center.
✕ Acne = Dirty Skin
Acne is driven by hormones and bacteria, not poor hygiene. Over-scrubbing strips oils and worsens sebum overproduction.
✕ All Dermatitis Is Allergic
Irritant contact dermatitis does not require prior sensitization: it occurs on first exposure to a strong irritant (e.g., bleach).
✕ Mixing Up Vesicles
Blisters in 2nd degree burns and contact dermatitis look similar but have different causes: thermal protein denaturation vs. immune-mediated spongiosis.

Summary Comparison

Feature Burns Acne Dermatitis
Primary layer Epidermis to hypodermis Dermis (pilosebaceous unit) Epidermis
Cause Thermal, chemical, electrical Hormones, bacteria, keratin Allergens, irritants, immune
Onset Immediate (acute) Gradual (chronic) Hours to days
Key feature Classified by depth (degrees) Comedones, papules, cysts Erythema, pruritus, vesicles
Healing Days (1st) to never (3rd) Weeks to months per episode 1 to 3 weeks after trigger removed
Scarring risk High (2nd/3rd degree) Moderate (nodular/cystic) Low (unless chronic scratching)

Question 1 of 5

A patient has a burn that appears white and leathery, with no pain reported at the burn site. What degree of burn is this most consistent with?

Question 2 of 5

Which of the following is the primary bacterium involved in the inflammatory response of acne vulgaris?

Question 3 of 5

A sharply demarcated, vesicular rash appears on a patient's hand 48 hours after wearing latex gloves. This delayed reaction is classified as which type of hypersensitivity?

Question 4 of 5

Using the Rule of Nines, a patient with burns covering the entire front torso and one complete arm has approximately what percentage of TBSA affected?

Question 5 of 5

What distinguishes irritant contact dermatitis from allergic contact dermatitis?