The science of medicine made a giant leap across the world with the advent of Islam in Iran and thorough the contributions of prominent Iranian polymaths such as Muhammad ibn Zacharia Razi in the 10th century as well as Hakim Ibn Sina (Avicenna) and Esmaeil Jorjani in the 11th century.

Similar to the Graeco-Arabic medicine, the Iranian traditional medicine is based on the theory that the human body is filled with four basic substances, called humors, including Phlegm (Balgham), Blood (Dam), Yellow bile (Ṣafra) and Black bile (Sauda). The four substances determine the physical and mental characteristics of each person, also known as mizaj or temperaments.

When the four humors are in balance, it will bring about physical and mental health. However, any excess or deficiency of any of the four bodily fluids in a person will result in diseases and disabilities.

Zacharia Razi developed the four temperaments into an elaborate medical system and Hakim Ibn Sina meticulously explained the detailed knowledge of four humors in his medical encyclopedia The Canon of Medicine.

According to the Iranian medcine, mizaj signfies the excess or lack of four main qualities in a person’s body, including warmness, coldness, dryness and wetness, and those specific qualities construct all physical or mental characteristics of a person.

Mizaj and genetics are relatively similar as the temperament  will be determined once an embryo starts to develop. Morover, the dominant mizaj  can be inheried from the the parents.

As far as the dominance of mezaj is concerned, tempers are classified into nine categories of warm, cold, wet, dry, warm and dry, warm and wet, cold and dry, cold and wet, and moderate.

The key strength of the Iranian traditional medicine is that it prioritizes health maintenance in individual lifestyle over treating diseases. Recognition of an individual’s temperament is considered the first source of information for maintenance of one’s optimum health and diagnosis of their illnesses.

The life style rules in Iranian traditional medicine are mainly focused on six core principles, including food and drinks, climatic conditions and environment, sleeping and waking, physical activities, psychiatric conditions and ridding body from waste materials (sweat, urine or feces).