* Hair type: Fine, curly, oily, or dry hair can be more prone to bad hair days.
* Hair length: Longer hair can be more difficult to manage.
* Weather: Humidity, wind, and rain can all negatively affect hair.
* Hair care routine: Inadequate or improper hair care can lead to bad hair days.
* Personal perception: What one person considers a bad hair day, another might not mind.
However, it's safe to say that a significant portion of women (and men) experience bad hair days from time to time. Some surveys suggest that it is quite common, possibly affecting over 70% of women regularly.
In conclusion, while an exact percentage is impossible to give, it's reasonable to say that a large majority of women experience bad hair days occasionally.