This episode explores pathology of the skin as disease of interface and signalling. The skin is the largest organ of the body and the first point of contact with the external environment. It functions simultaneously as a physical barrier, an immune organ, a sensory surface, and a marker of internal health. Disease of the skin is therefore often both local and systemic.
The episode begins with normal skin structure, emphasising the layered organisation of epidermis, dermis, and subcutis. Keratinocytes, melanocytes, Langerhans cells, and adnexal structures are presented as an integrated defensive and regenerative system. Rapid epidermal turnover is highlighted as both protective and vulnerable to dysregulation.
Inflammatory skin diseases are examined first. Dermatitis, psoriasis, and immune mediated rashes are explored as disorders of immune signalling and barrier dysfunction rather than simple irritation. The episode highlights how cytokine driven inflammation alters epidermal differentiation and produces characteristic clinical patterns.
Infectious diseases of the skin are then explored through patterns of involvement. Bacterial, viral, and fungal infections are examined in terms of depth, spread, and host response. The skin is shown to act as both a barrier and a battlefield, where breaches allow rapid escalation of disease.
The episode then turns to disorders of pigmentation and adnexal structures. Melanocyte dysfunction is explored as cause of both hypo and hyperpigmentation, while hair follicle and sweat gland pathology illustrates how specialised structures reflect systemic and local disease.
Cutaneous neoplasia forms a major focus. Basal cell carcinoma, squamous cell carcinoma, and melanoma are examined as malignancies shaped by cumulative exposure and cellular origin. Melanoma is presented as a particularly aggressive cancer where early invasion and metastasis define outcome, reinforcing the importance of depth and spread over size alone.
Finally, the episode reframes skin pathology as visible medicine. Cutaneous signs often reveal internal disease, nutritional deficiency, immune dysfunction, and malignancy. The skin is presented not as superficial, but as diagnostically rich and biologically complex.
Key takeaways
* The skin functions as barrier, immune organ, and diagnostic surface
* Inflammatory skin disease reflects immune dysregulation
* Infection patterns depend on depth and host response
* Skin cancers arise from distinct cells with different behaviours
* Cutaneous signs often signal systemic disease
