Humidity season is here, and if your hair has its own opinion about the weather, you're not imagining it. Frizz isn't a flaw — it's physics. And once you understand what's actually happening at the strand level, you can stop fighting your hair type and start working with it.

Frizz Is Structural, Not Random

Here is the science: Hair is made primarily of keratin, a strong structural protein that naturally absorbs and releases water. On humid days, keratin draws moisture from the air into the hair shaft. As the hair absorbs that extra water, it swells, temporarily changing the hydrogen bonds that help determine your hair's shape. If moisture enters unevenly, the cuticle can lift, leading to frizz, puffiness, or a loss of definition. How much this happens depends on your hair's structure, which is why straight, wavy, curly, and coily hair each respond differently to humidity.

That's also why a one-size-fits-all anti-frizz product rarely works for everyone in the room. Straight hair, wavy hair, curly hair, and coily hair each let moisture in and let it out differently, which means each one needs a different defense.

As hair type experts, this is the exact problem we built Function of Beauty around: structure-matched care, not guesswork.

How Frizz Shows Up by Hair Type

• Straight hair lies closest to the scalp, so it tends to pick up humidity fast and go flat or limp rather than visibly frizzy, though flyaways are still frizz's cousin. Straight hair's sebum (its natural oil) distributes easily down the shaft, which is great for shine but means it can look greasy before it looks frizzy.

• Wavy hair sits between straight and curly. It has more volume than straight hair but less natural definition than curly hair, which makes it prone to both frizz and a kind of directionless puff when humidity hits.

• Curly hair has a curled hair shaft that affects how oil travels from root to tip. That uneven oil distribution is why curls can look dry and frizzy at the same time. It can be one or the other, or both, for a structural reason.

• Coily hair has the tightest curl pattern and the most cuticle separation, making it both the most porous and the most fragile hair type. Sebum can't really navigate those tight coils. This leaves the hair chronically dry. When dry, the outer layer (cuticle) lifts, allowing humidity from the air to enter the shaft, causing the strands to swell and expand

Matching Your Hair Routine to Your Hair Structure

This is why we created our Hair Type Collections. Every shampoo and conditioner, leave-in treatment, and mask is formulated with the unique characteristics of straight, wavy, curly, and coily hair in mind, helping each hair type respond better to humidity with the moisture, lightweight care, or nourishment it needs.

• Straight Hair Shampoo & Conditioner, with coconut water and avocado oil, are built to cleanse and hydrate without weighing strands down — because straight hair doesn't need heavy moisture, it needs balance.

• Wavy Hair Shampoo & Conditioner, with fermented rice water and argan oil, target the smooth-and-strengthen combo wavy hair needs to hold its shape instead of frizzing into a halo.

• Curly Hair Shampoo & Conditioner, with flaxseed extract and Brazilian pracaxi oil, hydrate while gently cleansing, which helps curls stay defined instead of fighting both dryness and frizz at once.

• Coily Hair Shampoo & Conditioner, with chia seeds and Jamaican black castor oil, deliver the intensive moisture coily hair needs from root to tip, since it can't rely on its own sebum to do that work.

If you're curly or coily, this is also a great season to lean on our Co-Wash. It's gentler than a full shampoo and lighter than a conditioner, so it won't strip the moisture your curls are working hard to hold onto.  We recommend alternating it with your shampoo to keep your scalp clean without over-drying your strands.

Twice a week, for any hair type dealing with humidity-related dryness, our Hair Mask gives you a deeper dose of conditioning with ingredients like shea butter, jojoba ester, and argan oil that go to work for 5 to 10 minutes to help reinforce the cuticle layer that humidity loves to disrupt.

The Last Line of Defense: Sealing It All In

Once your cleanse-and-condition routine is structure-matched, the final step is locking that moisture in before it has a chance to escape or before outside humidity has a chance to get in. For most hair types, that means a styling product that seals the cuticle rather than just sitting on top of it.

If you've got a specific frizz-prone day ahead of you — a wedding, a humid vacation, a big presentation and want something built around your exact hair goals, our Custom Hair Serum is formulated to reduce frizz by 70% and protect against thermal damage up to 400°F, with your choice of hair goals layered in. It's a nice option to have in your back pocket for the days your regular routine needs backup.

The Takeaway

Frizz isn't a sign your hair care routine is failing; it's your hair's structure responding to its environment exactly the way it's built to. The fix isn't more product; it's the right product for your specific hair type. That's the whole idea behind Function of Beauty: we don't guess at what your hair needs. We start with the structure and build from there.

Take the quiz, find your hair type collection, and let your hair do less work fighting the humidity this summer.