What causes hair to frizz?
The primary cause of frizzy hair is dryness. But, there are lots of other different factors that can dry your hair out and exacerbate frizz, such as:
Humidity
Humidity is the likely reason your hair gets frizzy, especially during summer (or when you are on vacation somewhere warm).
The dry cuticle becomes rough and open for humidity, explains Monica Davis [3], a professional hairstylist. As a result, a humid environment makes overdried hair frizzy since the outer layer starts soaking the moisture from the air and swells.