Due to the biological traits of Egyptian chamomile flowers (Matricaria chamomilla L.), their essential oil is a valuable natural raw material that is used in food preservation and pharmaceutical industries. Essential oil composition varies significantly with flowering stages. This study set out to characterize the essential oil composition of Egyptian chamomile flowers, which were created during the stages of initiation, differentiation, onset, fullness, end, and maturation. Using Clevenger-style approach, essential oils from various blooming phases were separated; however, gas chromatography and gas chromatography–mass spectrometry were used to identify their contents. Results were subjected to one-way analysis of variance. Flower yields and composition of essential oils varied throughout the different stages of bloom. The main chemical group of flower essential oils that was obtained throughout different stages of flowering was oxygenated sesquiterpenes, whereas the main constituents were α-bisabolol oxide A, α-bisabolol, and chamazulene. The highest levels of flower yield (2.1 and 0.9 kg m−2 for fresh and dry weights), essential oil output (0.9% or 8.1 g m−2), oxygenated sesquiterpenes (77.3%), α-bisabolol oxide A (38.7%), α-bisabolol (17.4%), and chamazulene (15.9%) were reported in flowers that were harvested at the fullness stage. This study showed that the variations in chamomile essential oil were caused by the plant's reliance on flowering stages, which means that variations in its biological activity are to be expected; however, chamomile essential oil is mainly used in the manufacture of some fragrances, perfumes and soaps. Also it is used to preserve food and make drugs for skin diseases, cancer, and issues with cardiovascular and immune systems.
