linguistic:paraphrasing, quality:corruption, quality:correction, structural:expansion
Middle East

Islam stresses the importance of cleanliness and personal hygiene. Islamic hygienical jurisprudence, which dates back to the 7th century, has a number of elaborate rules. Taharah (ritual purity) involves performing wudu (ablution) for the five daily salah (prayers), as well as regularly performing ghusl (bathing), which led to bathhouses being built across the Islamic world. Islamic toilet hygiene also requires washing with water after using the toilet, for purity and to minimize pathogens.

In the Abbasid Caliphate (8th–13th centuries), its capital city of Baghdad (Iraq) had 65,000 baths, along with a sewer system. Cities and towns of the medieval Islamic world had water supply systems powered by hydraulic technology that supplied drinking water along with much greater quantities of water for ritual washing, mainly in mosques and hammams (baths). Bathing establishments in various cities were rated by Arabic writers in travel guides. Medieval Islamic cities such as Baghdad, Córdoba (Islamic Spain), Fez (Morocco), and Fustat (Egypt) also had sophisticated waste disposal and sewage systems with interconnected networks of sewers. The city of Fustat also had multi-storey tenement buildings (with up to six floors) with flush toilets, which were connected to a water supply system, and flues on each floor carrying waste to underground channels.

A basic form of contagion theory dates back to the Persian medicine in the medieval, where it was proposed by Persian physician Ibn Sina (also known as Avicenna) in The Canon of Medicine (1025), the most authoritative medical textbook of the Middle Ages. He mentioned that people can transmit disease to others by breath, noted contagion with tuberculosis, and discussed the transmission of disease through water and dirt. The concept of invisible contagion was eventually widely accepted by Islamic scholars. In the Ayyubid Sultanate, they referred to them as najasat ("impure substances"). The fiqh scholar Ibn al-Haj al-Abdari (c. 1250–1336), while discussing Islamic diet and hygiene, gave advice and warnings about how contagion can contaminate water, food, and garments, and could spread through the water supply.

In the 9th century, Ziryab invented a type of deodorant. He also promoted morning and evening baths, and emphasized the maintenance of personal hygiene. Ziryab is thought to have invented a type of toothpaste, which he popularized throughout Islamic Iberia. The exact ingredients of this toothpaste are not known, but it was reported to have been both "functional and pleasant to taste."