Don't get us wrong; we're all about embracing the volume and softness that comes with frizzy curls. But sometimes we appreciate the option to enjoy a more defined look, even when humidity levels are off the charts.It's no secret that sticky summer air leads to frizz, but it's not the only culprit behind curls that won't hold their shape. If you find yourself asking, "Why is my hair so frizzy?" take a peek at these five common issues - because learning what causes frizzy hair is the first step to knowing how to tame it.1. Over-CleansingJust like skin, hair has a natural protective barrier that helps keep essential moisture inside and acts as a shields against the elements. Aggressive cleansers strip curly hair of this barrier, leading to dryness, breakage, and frizz. To keep your curls frizz-free, choose a sulfate-free shampoo, and avoid washing your hair every day. Instead, co-wash or simply rinse your hair with water between shampoos, and only cleanse when your scalp is actually dirty.2. DrynessLike a sponge, hair that's thirsty will try to soak up moisture wherever it can find it. This means that the drier your hair, the more susceptible it is to absorbing frizz-causing humidity from the atmosphere. Keep your curls well-hydrated by using a conditioner made for your curl type.3. An Open CuticleCurly hair's curving shape means its cuticle layer is naturally raised, with gaps in between the overlapping cells. These gaps allow moisture and nutrients to escape, and humidity to enter.To ward off frizz and help curls look healthier and shinier, you need to seal your hair's cuticle. Conditioners and moisturizing stylers can help with this, including those from our Advanced Climate Control collection. These products have nano-sized silk protein technology that helps to fill in gaps in the cuticle to defend against frizz.4. DamageYou know that cuticle layer we just talked about? Damage from environmental aggressors can compromise it, too. Heat, UV rays, and even friction from combing and brushing all make hair weaker and more prone to becoming frizzy. To prevent damage, use a priming spray to protect hair from sun, styling, and tangles.5. HumidityThis is the big one, but you already knew that. Nothing makes curly hair turn frizzy faster than rainforest-like conditions. That's because humidity disrupts the hair's internal hydrogen bonds, causing curls to shrink, frizz, and lose their definition. Luckily, the right anti-frizz styler can help.