When curls look defined one day and frizzy the next, the cause is not always a product problem. Weather changes can alter how hair holds its shape, how quickly it dries, and how much frizz appears—especially in curly hair.
This guide explains what is happening (in plain terms), how humidity and dew point relate, and which adjustments often help in different conditions.
What humidity does to curly hair (the simple science)
Hair is made largely of keratin proteins. Those proteins form temporary bonds that help hair hold a shape. When the air is humid, water molecules interact with hair and can change those temporary bonds. The practical result is that hair can swell, the cuticle can lift slightly, and curls can become less predictable—sometimes tighter, sometimes puffier, often frizzier.
A useful mental model:
- More moisture in the air can mean more water entering the hair fiber.
- That can mean more swelling, and more strand-to-strand friction.
- In curls, small changes in strand shape show up quickly as frizz or loss of definition.
Source note: Smithsonian’s explainer summarizes the hydrogen-bond mechanism and why humid air changes hair shape.
Humidity vs. dew point: why both matter
Humidity (relative humidity) tells how much water vapor is in the air relative to what that air could hold at that temperature.
Dew point is different: it is the temperature at which air becomes saturated and water starts condensing. Many curly hair routines use dew point as a practical “frizz predictor” because it correlates with how moisture-heavy the air feels.
A simple takeaway:
- High dew point often means the air is moisture-heavy, and hair is more likely to swell and frizz.
- Low dew point often means the air is dry, and hair may lose flexibility and feel rough or brittle.
(Dew point guidance is widely used in curly-hair communities; it is useful as a practical heuristic, not a strict scientific threshold.)
Why porosity changes the weather story
Porosity describes how easily hair absorbs and holds water. When the cuticle is more “open” (often described as higher porosity), hair tends to take in moisture more quickly—and can also lose it quickly.
In practice:
- Higher porosity hair often reacts strongly to humid air because water can enter more easily, increasing swelling and frizz.
- Lower porosity hair may resist humidity more, but can feel dry in low-humidity environments and may struggle with product absorption.
For a porosity refresher:
What temperature changes (and what it doesn’t)
Temperature matters for two reasons:
- Heat and dryness often travel together. Hot air can be dry, and dry air tends to pull moisture out of the hair surface faster.
- Cold air can reduce flexibility. Many people notice more roughness, tangling, and breakage risk in colder months—often because of lower humidity, friction from clothing, and less consistent conditioning.
It can be hard to separate “temperature” from related factors like indoor heating, wind, and routine changes. It is often more accurate to think in combinations:
- Hot + humid: swelling + frizz pressure.
- Hot + dry: dehydration + brittleness pressure.
- Cold + dry: static, tangling, and dryness pressure.
Product strategy in high humidity (when frizz rises)
In high humidity, many routines work better when the priority is film-forming hold and cuticle sealing over pulling in extra water.
Practical adjustments that often help:
- Go lighter on strong humectants if results become less stable. (A common example is glycerin.)
- Add a stronger hold layer (gel or mousse) to reduce strand movement as hair dries.
- Use a sealant layer (some oils, some silicones, or silicone-like polymers) in routines that tolerate them.
Why the “depends” matters:
- Some hair responds well to humectants even in humidity.
- Some hair frizzes immediately.
In strict Original CGM routines, some film-formers may be limited (especially non–water-soluble silicones). In low-poo or co-wash routines, the key question often becomes removability and buildup management over time.
Product strategy in low humidity (when hair feels rough or brittle)
In dry conditions, the problem is often the opposite: curls may lose flexibility, feel rough, or look dull.
Practical adjustments that often help:
- Increase water-based hydration (leave-ins, sprays) and apply to very wet hair.
- Use conditioning layers strategically (a conditioner + a lightweight leave-in) instead of one heavy product.
- Reduce friction (microfiber towel, satin bonnet/pillowcase) to keep the cuticle from getting roughed up.
Styling techniques that tend to be more stable across weather
Technique is not “scientifically settled” in a strict way, but some patterns are consistently useful:
- Apply stylers to very wet hair to improve distribution and reduce uneven drying.
- Use a structured drying approach (plopping, careful diffusing, or controlled air-drying) rather than constant touching.
- Avoid over-manipulation while drying. More touching often equals more frizz.
For diffusing specifically, the evidence is mostly practical rather than clinical. A safe framing is:
- Lower heat and less agitation often reduces visible frizz, but settings depend on hair density, porosity, and time constraints.
How routine choice changes what “humidity-proof” means
Even though weather affects hair broadly, the routine influences how well buildup can be managed and how stable “frizz control” feels over time.
A practical way to think about it:
- Original CGM (binary rules): Some film-formers are avoided, so routines often lean more on technique + water-soluble hold.
- Low-poo routines: Gentle surfactants can remove more film-formers, so stronger anti-humidity styling can be workable—if accumulation stays manageable.
- Co-wash routines: Because cleansing is milder, film-formers that help with humidity can also build up faster. Occasional deeper cleansing may be required.
Clarifying is not a “routine” by itself. It is a maintenance tool to remove buildup when regular cleansing is not enough.
If buildup is part of the frizz pattern, these references are useful:
How Bönpello’s routine modes affect ingredient decisions
Bönpello’s ingredient scanner is designed around the idea that ingredient suitability is routine-dependent, not universal.
In practice, the same ingredient can be interpreted differently depending on the cleansing context:
- Original CGM mode tends to reflect the common modern binary rule set used by many checkers.
- Low-poo mode evaluates whether ingredients are likely to be removable with gentle shampoo use and flags accumulation risk over time.
- Co-wash mode assumes conditioner-based cleansing and is typically more restrictive about film-formers and buildup-prone ingredients, because removal can be harder without shampoo surfactants.
This does not mean an ingredient is “good” or “bad.” It means the same ingredient can create different trade-offs depending on how cleansing is done.
Example: anti-humidity film formers vs. removability
In humid conditions, film-forming ingredients can help reduce frizz by limiting how much water moves in and out of the hair fiber during drying.
Examples of film formers include some polymers (such as certain polyquaterniums) and some silicones. These can improve smoothness and definition for many curl types.
The trade-off is that some film formers can also be harder to remove in routines that rely on milder cleansing—especially co-wash routines. In those cases, the same “anti-humidity” strategy can increase buildup risk, and the routine may need occasional stronger cleansing (clarifying) to stay balanced.
A simple checklist: what to change first
For quick testing without rewriting an entire routine:
- Change one variable at a time (product OR technique OR frequency)
- Track the weather context (humidity + dew point, if used)
- Watch for the signal
- More frizz during drying = technique/hold issue
- Frizz after a few days = buildup or moisture balance issue
- Limp curls in humidity = often too much softening, not enough structure
Summary
Environmental factors can change how curly hair behaves even when products stay the same. Humidity and dew point tend to influence moisture uptake (swelling and frizz), while dry conditions often increase roughness and brittleness. Porosity helps explain why one routine works for one person but fails for another.
A reliable approach is not chasing perfect weather-proof curls. It is understanding the levers—moisture, film-forming hold, removability, and technique—so routine adjustments can be made when conditions change.
