Fundamental fact about this disease: Plague Psoriasis

A common knowledge-base portal via Wikipedia provides just enough knowledge.
I like webmd better as it looks closer to scientific oriented write up.
The Mayo Clinic would provide much thorough and unbiased explanation for the disease.

From Mayo Clinic, Psoriasis triggers

Psoriasis typically starts or worsens because of a trigger that you may be able to identify and avoid. Factors that may trigger psoriasis include:

	
Infections, such as strep throat or skin infections
	
Injury to the skin, such as a cut or scrape, a bug bite, or a severe sunburn
	
Stress
	
Smoking
	
Heavy alcohol consumption
	
Vitamin D deficiency
	
Certain medications — including lithium, which is prescribed for bipolar disorder, high blood pressure medications such as beta blockers, antimalarial drugs, and iodides

All about autoimmune related issues

Wikipedia on TNF-alpha, a cancer related protein: Tumor Necrosis Factor alpha