∎ Macula: localized color change, neither raised nor sunken; diameter <1cm (large lesions formed by dense fusion of macula are called patches); including inflammatory and non-inflammatory erythema , petechiae (diameter <2mm) and petechiae (diameter >2mm), pigment abnormalities (such as hyperpigmentation, hypopigmentation and depigmentation)

Papula: a substantial bulge above the skin surface; diameter <1cm; can be primary or secondary to macules; can subside on its own or transform into herpes/pustules; most are infiltrated by skin inflammation Or epidermal hyperplasia, and a few are caused by the deposition of metabolites; slightly raised papules with flat surfaces are called maculopapules, and flaky lesions formed by the fusion of a large number of dense papules are called plaques.

Vesicle: a lacunar lesion that is higher than the surface of the skin and contains fluid; it varies in size, with a diameter >0.5cm (Human Health Edition: diameter >1cm); it is called a bulla; most are caused by an inflammatory reaction It can also be caused by the dissolution and destruction of the adhesive substance between spinous cells (pemphigus) or basement membrane lesions (dermatitis herpetiformis); it can be divided into intraepidermal blisters (such as prickly heat, herpes simplex, pemphigus) and subepidermal blisters ( Such as erythema multiforme, pemphigoid); there may be redness around the deeper blisters, and there will usually be no scars after healing; if the cell edema in the epidermis of the papule is obvious, small blisters may form on the top, which is called papulovesicle

Pustula: a blister containing pus, surrounded by redness; it can be primary or secondary to blisters, mostly caused by purulent bacterial infection; the location varies in depth; there is usually no scar after healing

Wheal: Acute, temporary, localized, edematous, and raised damage to the superficial dermis. It usually subsides within a few to more than ten hours without leaving any trace. It is often accompanied by severe itching; it may appear light red/ Pale, with redness around it and irregular edges; seen in urticaria

∎ Nodule: round, localized, substantial damage to the dermis/subcutaneous tissue. It can be higher than the skin surface or located under the skin and can only be palpated. It varies in size and is hard to touch; it can be caused by inflammation of the subcutaneous tissue. (such as erythema nodosum), vascular inflammation, metabolite deposition (such as nodular xanthoma), parasitic infection, tumors, etc.

∎ Cyst: a cystic lesion containing liquid/viscous/cellular components with a certain wall structure in the dermis/subcutaneous tissue. It can be higher than the skin or only palpable; it can feel elastic to touch; seen in sebaceous glands Cysts etc.

Scale: Shedding of the epidermal cuticle caused by hyperkeratosis, parakeratosis, drying of blisters, etc.; it can be in the form of pityriasis (pityriasis versicolor), oyster shell (psoriasis), or large flakes ( exfoliative dermatitis)

 Crust: An attachment formed by the mixture and drying of serous fluid, pus exuded from skin damage, tissue microorganisms exuded from blood necrosis, etc.; can be thin or thick, soft/brittle in texture, attached to the wound surface; includes pus scab, serous scab, bloody scab

∎Maceration: The skin has been immersed in water for too long or has been in a humid environment for a long time → the cuticle absorbs too much water and the epidermis becomes soft, white and wrinkled; it is more common in wrinkles such as between the fingers (toes); epidermis can occur when exposed to mechanical factors fall off, form erosion

Erosion: Superficial defect of epidermis/mucosa, exposing red moist surface, healing quickly without leaving scars

Ulceration: a localized defect of the skin/mucosa involving the dermis/subcutaneous tissue. There may be serous fluid, pus, necrotic tissue, and scab attached to the surface. The edges are often irregular; scars remain after healing.

Scratching/exfoliation: linear skin lesions caused by scratching, often involving only the epidermis and leaving no scars after healing

Fissure/Cracks: Linear cracks in the skin, often deep into the dermis, with pain and bleeding; often caused by skin inflammation, thickening of the stratum corneum or dry skin, resulting in reduced skin elasticity and increased fragility, and are caused after traction; common It is found on the palms, soles and finger (toe) joints, consistent with skin lines, and can also be seen at the corners of the mouth, lower part of the breast, and perianal area.

Scar: formed by new connective tissue filled after ulcer healing, with smooth surface without striae, hair and other appendages, and inelasticity; divided into proliferative (such as keloid) and atrophic (such as lupus vulgaris)

Atrophy: skin degeneration caused by inflammation, endocrine changes, and radiation; divided into epidermal atrophy (skin thinning, translucent, parchment-like surface but normal texture), dermal atrophy (local skin depression, surface texture may be normal) , hair can become thinner/disappear), mixed type

Lichenification: localized skin thickening, roughness, increased surface texture (in a grid-like pattern), often accompanied by severe itching; mainly caused by thickening of the stratum corneum and spinous layer due to frequent scratching or friction, seen in Chronic pruritic skin disease

[1] Patch test: used to check allergens; conducted under standard conditions, observed after 48h and 72h

[2] Scratch test: used to check whether the tested allergen can cause type I allergic reaction, observed within 15~30 minutes

[3]Intracutaneous test