7. At formal appearances, royal women are expected to wear hats.

Reason: It’s a long-standing custom that originated when women were not supposed to display their hair in public.
Exception: After-hours activities and casual gatherings
One of the most persistent parts of the British monarchy’s intriguing history of dress etiquette is the expectation that royal women wear hats to formal engagements. This custom dates back to a period when women were not supposed to display their hair in public since it was seen as unsuitable and unfeminine.
At formal appearances, royal women are expected to wear hats. © Shutterstock/TThomas Dutour
The hats, which are frequently ornate and fashionable, have come to define royal attire. This regulation is not unchangeable, though. At less formal events or in the evening, royal women frequently decide to forgo their headgear in favor of tiaras.