Outside Humidity & Perm

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Q: Does outside humidity have any effect on how a perm takes?
A: No. In fact this becomes obvious when you consider that most perms involve wrapping freshly shampooed hair on perm rods while the hair is still wet. The minimal levels of moisture introduced by outside humidity are completely insignificant compared to the fact that the hair is totally saturated already.
In fact, you want the hair to still be pretty damp when you begin applying the perming solution so that it is distributed evenly throughout the hair. If the hair were dry when the perming solution was applied, the hair would soak up the solution where it came in contact with the hair. With hair that is already saturated by water, the solution spreads throughout the water in the hair and equalizes the level of solution for an even coverage and even processing.
There are factors that will affect how well a perm takes. The cleanliness of the hair, the condition of the hair, and the hair's porosity all play a role in how well the hair receives the chemicals that reshape the curl. If the hair is dirty or has product build-up, it can prevent the perm solution from penetrating the hair shaft and can prevent good perm results.
The same is true if the hair has low porosity (also known as being resistant). Often gray hair has low porosity because the act of the hair going gray often results in a tightening of the cuticle layer preventing the passing of moisture into and out of the hair.
Finally, if the hair is already damaged or is in poor condition, it may lack sufficient elasticity (or basic structural integrity) to withstand the perming process. If you are concerned about perming your hair, don't hesitate to seek the aid of a professional.
See also:
Perms and perming hair
Will humidity affect a perm?
How to maintain your hairstyle in humid weather
Are there any chemicals in a perm that will be affected by high humidity?