Humid air causes hydrogen bonds to form between water molecules and the proteins in your hair, triggering curls and frizz.

If you have long hair, you probably don’t need to look up a weather report to get an idea of how much humidity’s in the air: You can simply grab a fistful of hair and see how it feels. Human hair is extremely sensitive to humidity—so much that some hygrometers (devices that indicate humidity) use a hair as the measuring mechanism, because it changes in length based on the amount of moisture in the air.

Straight hair goes wavy. If you have curly hair, humidity turns it frizzy or even curlier. Taming the frizz has become a mega industry, with different hair smoothing serums promising to “transform” and nourish hair “without weighing hair down.” But just why does humidity have this strange effect on human hair?

Hair Cross Section

Hair’s chemical structure, as it turns out, makes it unusually susceptible to changes in the amount of hydrogen present in the air, which is directly linked to humidity. Most of a hair’s bulk is made up of bundles of long keratin proteins, represented as the middle layer of black dots tightly packed together in the cross-section at right.

These keratin proteins can be chemically bonded together in two different ways. Molecules on neighboring keratin strands can form a disulfide bond, in which two sulfur atoms are covalently bonded together. This type of bond is permanent—it’s responsible for the hair’s strength—and isn’t affected by the level of humidity in the air.

But the other type of connection that can form between adjacent keratin proteins, a hydrogen bond, is much weaker and temporary, with hydrogen bonds breaking and new ones forming each time your hair gets wet and dries again. (This is the reason why, if your hair dries in one shape, it tends to remain in roughly that same shape over time.)

Hydrogen bonds occur when molecules on neighboring keratin strands each form a weak attraction with the same water molecule, thereby indirectly bonding the two keratin proteins together. Because humid air has much higher numbers of water molecules than dry air, a given strand of hair can form much higher numbers of hydrogen bonds on a humid day. When many such bonds are formed between the keratin proteins in a strand of hair, it causes the hair to fold back on itself at the molecular level at a greater rate.

On the macro level, this means that naturally curly hair as a whole becomes curlier or frizzier due to humidity. As an analogy, imagine the metal coil of a spring. If you straighten and dry your hair, it’ll be like the metal spring, completely straightened out into a rod. But if it’s a humid day, and your hair is prone to curling, water molecules will steadily be absorbed and incorporated into hydrogen bonds, inevitably pulling the metal rod back into a coiled shape.

Click here to find out on how to help prevent Puffy Hair in Humid Weather

Bleaching can leave your hair with mild to severe damage due to acidic action of strong chemicals or wrong handling or extreme heat application during the procedure. The ruined hair might feel dry, spongy, porous, brittle or rough due to damaged hair cuticles which cover the cortex, carrying the hair’s natural color. While store-bought potion and products might help repair the condition, there are quite a few easy, natural ways to get your hair healthy after bleaching.

1. Shampoo your hair less often. In order to restore your bleached hair, you will have to discontinue washing your hair daily. When you shampoo your hair, you are not only cleaning the hair but you are also stripping the natural oils and sebum from your hair. The oils and sebum are natural moisturizers. If your hair is prone to looking and feeling oily, use a dry shampoo on the days that you don’t wash your hair.

2. Deep condition your hair one or more times per week. The amount that you condition your hair depends on how often your hair needs it. Apply deep conditioner to your hair after you have already washed it with shampoo and regular conditioner. Use a wide-toothed comb to distribute it through your hair. Warm a towel in the dryer or with a hair dryer. Wrap your hair with the warm towel. Leave the deep conditioner and towel on your hair for 30 minutes. Wash it completely out of your hair.

3. Always wash hair with lukewarm or cold water. Hot water promotes dryness in the hair. That is counterproductive to restoring bleached hair as your goal is to add moisture to your hair. If you wash hair with lukewarm water, always rinse your hair with cold water at the very end. That will seal the cuticle.

4. Use a leave-in conditioner after every time that you wash your hair. As bleached hair is often porous and prone to tangles, a leave-in conditioner adds moisture and makes hair easier to comb. That will prevent strands of hair from breaking off.

5. Do not use heat on your hair. Avoid using blow dryers, hot rollers, flat irons and curling irons. Heat is detrimental to restoring your bleached hair. If you are not willing to forego heat when styling your hair, it may be impossible to restore the hair.