Skin Injury Factors and Lesions

Primary lesions: Direct results of disease, crucial for diagnosis.
Secondary lesions: Evolve from primary lesions, usually less diagnostically significant.

Macule: Discolored area, ≤ 1 cm; example: lentigo, a benign hyperpigmentation.
Papule: Small, round, solid elevation, ≤ 1 cm in size.
Plaque: Larger, flat-topped solid elevation of the skin.
Nodule: Hard elevation, ≥ 1 cm, extends into deeper skin layers.
Vesicle: Circumscribed elevation of < 1 cm filled with clear fluid.
Bulla: Larger vesicle (> 1 cm) containing fluid within the epidermis.
Tumor: Large mass implicating neoplasia, affecting skin or subcutis.
Cyst: Epithelial-lined cavity with fluid or solid material.
Pustule: Small, pus-filled elevation of the epidermis.
Abscess: Accumulation of pus within epidermis or hair follicle.
Wheal: Smooth, well-defined elevation from dermal edema, commonly seen in allergic reactions.

Scale: Accumulation of flakes or dandruff on the skin surface.
Crust: Dried exudate, blood, or serum accumulation.
Comedo: Dilated hair follicle filled with cornified cells; often seen in conditions like hyperadrenocorticism.

Alopecia: Loss of hair.
Hypotrichosis: Less hair than normal.
Atrichia: Absence of hair due to failure of development.
Effluvium/defluxion: Excessive shedding.
Hypertrichosis (hirsutism): More hair than usual; can be due to endocrine disorders.

Hyperpigmentation: Increased melanin production, often due to inflammation or genetics.
Hypopigmentation: Reduced melanin, can be congenital or due to melanocyte dysfunction.
Pigmentation incontinence: Loss of melanin from the basal epidermis.

Epidermal collarette: Circular rim of keratin flakes after vesicle/pustule loss.
Ulcer: Break in the epidermis, exposing underlying dermis.
Excoriation: Erosions or ulcers from scratching or trauma.
Scar: Fibrous tissue replacing damaged skin.
Fissure: Linear cracks in thickened, inelastic skin.
Lichenification: Thickening and hardening of skin with visible superficial markings.