Humidity is water. The pH level of water is 7.0. Our body and hair's pH is usually around 4.5 to 5.0. The higher pH level of the water from the humidity can be enough to elevate the cuticle of the hair resulting in frizz if the cuticle is not sealed.
So how do you seal the cuticle?
If you are born with naturally straight hair (Type 1 hair), then congratulations!, your cuticles are naturally sealed shut. Your hair probably will not hold a curl without some extra hold spritz and a hot curling iron. Humidity should not affect your hair at all unless you damage your cuticle by using a hair chemical on it such as hair bleach, hair lightener, permanent color or a permanent wave. Mechanical tools can damage the cuticle as well if they are too hot.
So if the cuticle becomes damaged, condition it to repair, then seal the cuticle with either a semi-permanent color gloss or silicone based serums such as argan oil, etc. Joico has a Humidity Blocker spray that you can spray generously throughout the hair as well without worrying about stiffness.
So if you are born with any curl to your hair (Type 3 and Type 4 hair especially), then curls are prone to frizz because with every turn, there is an opportunity for the cuticle to raise.
If you are embracing your curls as a hairstyle, then a "defining" gel (hair product) can seal the hair strands and block the humidity from getting to the cuticle layer.
So back to the original question: Does Humidity cause frizz? Yes, if you have curly hair, chemically altered hair, or a damaged cuticle layer from heat styling.
How do hair chemicals damage your cuticle layer?
If you permanently alter your hair with a color treatment, relaxer, curly perm, soft curl, etc, then yes, these hair chemicals swell the cuticle to get into the hair strand to alter it, and is rinsed out and the pH level is neutralized to calm the cuticle back down. However, the cuticle layer will never shut completely back to its original state without some styling products or a sealant. Want to test this statement? Let your hair "air dry" without applying any product after completion of a hair chemical. If it dries without any frizz, then your cuticle was not damaged, and you should personally inform me because I really would want to know what type of hair you have that defies the rules. (At least, Comment below.)
Okay, back to the discussion, now that you understand what causes frizz . . . you can make better choices on hair products, styling tools, and handling of your hair.
Black and white photo above was from blog.tawkify.com
