With the onset of summer and hot, sticky weather, it’s time to talk about one of the most moisturizing (yet frustrating) product ingredients found in hair care products: humectants.

Humectants are included in many hair care product formulations to promote moisture retention within the hair shaft by absorbing water from the atmosphere. They can also slow down the evaporation of liquid, keeping moisture in the hair shaft for longer periods of time. Under ideal conditions, humectants help curly hair to retain its hydration and spring.

In less than ideal conditions, however, humectants can cause a world of problems if you aren’t aware of their possible drawbacks.

In very low moisture areas, dry climates, or during the wintertime, humectants can actually dry the hair out further by absorbing water from the hair itself when there is no moisture in the surrounding atmosphere. Because the sole purpose of a humectant is to find and absorb moisture, it will find it and take it wherever it can get it–and that includes yanking out the moisture from inside your curly locks, leaving you with a dry, frizzy mess.

In very high moisture areas, wet climates, or during the summertime, however, humectants will force overly porous hair to continuously “drink” water from the humid, moisture-laden atmosphere until the hair shaft is swollen, bloated and tangled. Products with heavy humectants are often the cause of the humidity-induced frizz common to many girls with curls in the hot, humid summertime.

Both overly dry and overly swollen hair can become frizzy and/or lose their wave pattern due to improper use of humectants. Depending on your hair type—and, most especially if you are overly porous—humectants should not be used in very dry or very wet climates, or when dew points indicate there is too little or too much moisture in the atmosphere.