The bacterium involved in the appearance of furuncle is Staphylococcus aureus. Many healthy people carry this bacteria, but do not develop a boil.
Several causes favor the appearance of a boil. Among them: poor hygiene (including use of a dirty razor), local infection, poor skin conditions, etc.Also, the maceration, the friction of the clothes, and the untimely manipulations (on pimples of acne for example) can cause the appearance of boils.
Health conditions, such as excessive sweating and obesity (due to skin folds) can be implicated, as other conditions favor the appearance of a boil.
Finally, on the occasion of an infection such as bacterial sinusitis, it can also appear an infection in the skin, a follicular infection (a boil).
Once the skin is contaminated, the boil is formed by a specific mechanism. When the staph becomes aggressive and multiplies, a physiological defense response of the body occurs: it is inflammation. It then appears redness, swelling, pain and the inflammatory region is hot.
The furuncle is formed: the pathogenic staph that has invaded the cutaneous zone causes necrosis (ie destruction) of the surrounding tissues - namely: the hair, the sebaceous gland, the cells of the skin. The body then produces white blood cells to defend itself against this intrusion.
Bacteria, white blood cells, necrotic tissue form a magma that constitutes what is called pus. It is collected little by little and gives then a yellowish pustule ready to be evacuated spontaneously: it is the bourbillon.