Cortisol is a corticosteroid hormone produced by the Zona fasciculata of the adrenal cortex (in the adrenal gland). It is a vital hormone that is often referred to as the "stress hormone" as it is involved in the response to stress.

Cortisol increases blood pressure, blood sugar levels and suppresses the immune system.

References

de Weerth C, Zijl R, Buitelaar J (2003). "Development of cortisol circadian rhythm in infancy". Early Hum Dev 73 (1-2): 39-52. PMID 12932892.?