Hera Hair Beauty · The Curl Papers
What Singapore's humidity really does to curly hair — and what the science says to stop believing.
By late morning in Singapore the air holds most of the water it can. Your curls, defined at 8am, have quietly rearranged themselves by 11 — softer at the crown, wider through the lengths, a halo where there was a spiral. It feels personal. It isn't. It is physics, and once you understand the mechanism, most of the frustration — and most of the internet's advice — falls away.
This is a plain, sourced account of how textured hair behaves in a climate that sits near 80% relative humidity for much of the year5, written by the people who cut and colour it every day. We have kept it honest: where the evidence is strong we say so, and where the popular wisdom is wrong we say that too.
Why your curls move through the day
Hair is mostly keratin, and keratin holds its shape through several kinds of bond. The strong ones — disulfide bonds — are set by your genetics and only changed by chemistry. The shape you can influence day to day is held by a far larger number of weak hydrogen bonds1.
Water breaks hydrogen bonds. A water molecule is unusually good at it — it can both donate and accept bonds — so as humidity rises, water moves into the hair and the temporary bonds holding your style let go and reform in a new position1. Hair is hygroscopic: it exchanges moisture with the air until the two reach balance. At around 30% humidity hair carries roughly 6% of its weight in water; near 70% that climbs to about 13–14%1.
Frizz is not caused by "too much" humidity. It is caused by change in humidity — every time the air and your hair renegotiate their balance.
This is why the relative humidity of the air — not the temperature, not the dew-point folklore — is the honest predictor of a frizz-prone day. It is the same measure the peer-reviewed curl-retention studies use2, and the one behind Hera's live Frizz index.
Why curls feel it more than straight hair
Every head of hair exchanges moisture with the air. Curls simply show it more. A curved strand tends to have a more elliptical cross-section, and its cuticle — the shingled outer layer — is stressed unevenly around the bends, so its scales sit less flat1. When moisture swings, that uneven surface lifts and catches the light as frizz, and the curl pattern, which depends on the internal bond arrangement, relaxes and re-tightens more visibly than a straight fibre ever would2.
It also means curly hair is, on average, drier along its length and more fragile at the bends — not because it lacks care, but because the same architecture that makes a curl beautiful makes it harder for the scalp's natural oils to travel down it. That is structure, not a failing, and it changes what actually helps.
What the internet gets wrong
Most curly-hair advice online is repeated so often it feels like fact. Much of it does not survive contact with the science. We say this not to be contrarian, but because chasing the wrong rules is where money and mornings are lost.
Find your porosity, then buy for it.
What the science says
"Porosity" online conflates two different things: genuine cuticle damage (real, and worth addressing) and an inherent trait of healthy hair (largely unsupported). The popular home tests don't reliably measure either. For healthy hair, your curl tightness, strand thickness and density predict what a product will do far better than a porosity label4.
Oils and butters seal moisture into the hair.
What the science says
They don't form a true seal. Oils sit on the surface as separate blobs with gaps that water vapour passes straight through4. They add slip, softness and shine — worth having — but they do not "lock in" water or lock out humidity. The internal water content of your hair is set by the humidity around you, not by what you layer on top1.
Cold water and heat "close" and "open" the cuticle.
What the science says
The cuticle does not open and close with temperature or water. Its scales are lifted meaningfully only by high-pH chemical processes — the kind that also damage the fibre4. A cold rinse can feel good and add momentary shine; it is not opening or shutting a door.
Avoid protein — and avoid humectants in humidity.
What the science says
Blanket rules rarely hold. Protein helps some hair and not others; avoiding all of it "because one product went wrong" is like avoiding all foods over one allergy4. And there is limited evidence that simple humectants can actually reduce breakage in tightly coiled hair — the opposite of the popular warning4. The truth is specific to your hair, which is exactly why a consultation beats a rule.
What actually holds a curl here
Strip away the myths and the honest levers are few, and mostly professional.
Sources
- Wong, M. — Hair frizz science: water and hydrogen bonds, and evidence-based hair care. Lab Muffin Beauty Science.
- Wortmann, F.-J. et al. — the humidity dependence of the keratin glass transition and dynamic-humidity curl retention (Biopolymers; Journal of Cosmetic Science).
- Breakspear, S. et al. — moisture sorption of human hair (International Journal of Cosmetic Science).
- Evidence-based critique of popular porosity and protein-/humectant-avoidance advice, drawing on the cosmetic-science literature (curlsbot.com, citing the above).
- National Environment Agency, Singapore — real-time relative humidity, data.gov.sg (open data).
Every scientific claim here is sourced or framed as general guidance. Where we could not stand behind a stronger statement, we made a softer one.
Hera Hair Beauty
Curl specialists since 2012 · Tanglin Mall & Quayside Isle, Sentosa Cove