It's summer and the place I live is even more humid than normal. I thought I would share some information about humidity, dew points, humectants, anti-humectants, etc. I hope you find this informative!

Relative humidity: The relationship between the vapor pressure or vapor density of the water in the air at a specific temperature versus the saturated vapor pressure of water at that temperature.

Dew point: A higher value for our dew point means a higher concentration of water vapor in the atmosphere, and a lower dew point means less moisture is in the air.

Humectants: Molecules that possess atoms and groups of atoms that attract and bind water to themselves. Examples: glycerin, agave nectar, honey, algae extract, hydrolyzed collagen, propylene glycol, butylene glycol, hyaluronic acid, sorbitol, glucose, fructose, and hydrolyzed proteins

Film Forming Humectants: Forms flexible barriers that retain water in your hair. These are safe to use in low dew points because of the film (cast) they form. Examples: flaxseed, okra, aloe vera, hydroxyethylcellulose, pectin, xanthan gum, guar gum, marshmallow root, slippery elm, carrageenan (also known as irish moss or seaweed extract, sea emollient, sea algae, sea vegetable), nettle leaf tea, nettle extract, panthenol, and hydroxypropyltrimonium honey

Anti-humectant: Does not attract water molecules to itself, water repellent/insoluble in water, and typically coats, flattens, and seals the external cuticle layer of the hair strands. Can also include emollients which are plant oils, but can cause buildup or be too heavy for certain hair types. Examples: silicones, esters (such as isopropyl palmitate), hydrogenated castor oil, beeswax, and plant triglycerides such as coconut oil, palm oil, olive oil, mango butter, cocoa butter, and shea butter.

Humidity Resistant Ingredients: Helps your hair tolerate excessive moisture in the air. Many of these ingredients do build up, you need to make sure you clarify regularly. Examples: polyquaternium-4, polyamide-1, polyquaternium-10, polyquaternium-69, polyquaternium-11, PVA/VP Copolymer, VP/DMAPA Acrylates Copolymer, polyacrylate acid, and polyacrylate-2 crosspolymer

Dew points below 35°F

A humectant applied to your hair might be irresistibly drawn to the moisture in your hair and make every attempt to steal it from you (by drawing it out of your hair and binding it to itself). This can result in dry, fly-away hair, split ends, and broken strands. You can combat this by using plenty of moisturizing products, not over-drying your hair (leave it somewhat moist after washing), and layering leave-in conditioners with humectant-containing styling product. Use leave in conditioners, light hold products, and plenty of emollients.

Dew points from 35°F to 60°F

Curly hair seems to really thrive in moderate climactic conditions, and dew point ranges of approximately 35°F to 50°F seem to be optimal. In this type of weather, most curlies find that they can get really pleasant results by using products that contain some humectants. There is just enough moisture in the air that the humectants can grab a little from the environment, which can enhance the curl and create a bouncy feeling to the hair.

Dew points of 60°F or above

Might be a good idea to apply some product with anti-humectant properties. These products will seal the hair shaft, flatten the cuticle and prevent atmospheric moisture from absorbing into the interior of your strands. Most of these products will contain ingredients that are water insoluble. However, many of these products contain ingredients which are easily removed with an extremely mild shampoo or perhaps even a thorough conditioner wash. May skip a leave in conditioner, use hard hold products like gels. may want to avoid humectants, and use emollients.

References from:

https://www.naturallycurly.com/curlreading/curl-products/humidity-humectants-and-the-dew-point

https://www.naturallycurly.com/curlreading/wavy-hair-type-2/the-411-on-dew-points-humectants

https://holisticenchilada.com/curly-girl-guide-weather-styling-dew-points-humectants/