Frequently Asked Questions

Fine, thin or bleached hair generally straightens at 250-300F; healthy fine hair at 300-330F; medium hair at 330-370F; thick or coarse hair at 370-390F. Published research reports cuticle degradation beginning around 302F and cortex damage from around 392F, so 450F is above every threshold in the literature. The full chart by hair type is here.

Published research on thermally treated hair reports cuticle degradation beginning around 150C (302F) and cortex damage from around 200C (392F). Critically, WET keratin denatures between 120C and 150C - far lower than dry - which is why ironing damp hair is categorically worse than anything else you can do. Full detail here.

No. This is the one hard rule on this site. Wet keratin is reported to denature between 120C and 150C, which is 248F to 302F, so a 350F plate on damp hair is operating well past the point of irreversible structural damage. Dry completely first, at any temperature setting.

Far less than an iron does. The dryers on this site that publish a figure top out between 212F and 230F, well below the roughly 302F at which cuticle degradation is reported. Most blow-dry damage is mechanical - fast air lifting cuticle scales - rather than thermal, which is why lower fan speed helps more than lower heat.

Not structurally. Nothing regrows cuticle or repairs a denatured cortex. Bond-building treatments and conditioners improve how the remaining structure behaves and feels, which is worthwhile, but the damaged length has to grow out. Any product described as repairing heat damage is describing a cosmetic improvement.

Yes. The American Academy of Dermatology's guidance is to use low or medium heat settings AND a product to protect hair from heat. The important caveat is that it buys margin at the temperature you were already using - it is not permission to turn the heat up. More here.

1,500W is the practical minimum for a full-size dryer and 1,875W is the US convention, which exists because a standard 120V 15-amp household circuit carries about 1,800W. Fine or short hair is well served by 1,200-1,500W. But wattage measures electricity consumed, not air moved, and air is what dries hair - the full explanation is here.

Neither in general - they suit different hair. Titanium transfers heat fast and recovers its set point quickly, which coarse resistant hair needs and which makes it unforgiving on fine hair. Ceramic heats more gently and evenly, which suits fine or damaged hair but dips under load on dense hair. Full comparison.

Ionic output neutralizes the static charge that builds on hair as it dries, which addresses one component of frizz. It does nothing about a cuticle damaged by heat or about humidity. And every dryer on this site has it in some form, so it stopped being a way to choose between them roughly a decade ago.

For shoulder-length hair, a 1-inch barrel gives a classic curl. 3/4 inch for tighter definition, 1.25 inch for loose waves. Remember curls loosen as they cool, so pick roughly one size smaller than your finished look. Full chart on the curling irons page.

For Europe, the UK, Australia and most of Asia, yes - unless you are prepared to lose the dryer. Those regions run at 220-240V against the US 110-120V, and a plug adapter only changes the shape of the plug, not the voltage. More on travel dryers.

The guard number is how many eighths of an inch it leaves. A #1 leaves 1/8 inch (about 3 mm), a #4 leaves half an inch (about 13 mm), an #8 leaves a full inch. Multiply the number by roughly 3 for millimeters. Full chart.

No, and every page says so. There is no lab here, no sample cupboard and no manufacturer relationships. What we do instead is compile every published specification, link each one to its source, and work through the arithmetic those specs support. The method is written down in full.

Because you can check them. Every specification row on every product carries a source link to the manufacturer page it came from, every calculation shows its formula and inputs, and the ranking criteria are published. If a figure here disagrees with the manufacturer, the manufacturer is right and we want to know.

Amazon Associates commission on qualifying purchases, at no extra cost to you. That is the whole model - no sponsored placements, no free products, no paid inclusion and no manufacturer relationships. Every pick also carries a 'skip this one if' section, which is a required field. Full disclosure.

No, and the reason is checkable rather than just asserted. Amazon pays the same rate across this whole category, so there is no commission incentive to prefer one product over another within it. Every product on the site also names the buyer it is wrong for - that is enforced by the content model, not by good intentions.

Because there are no customers. Heat Index is a publication, not a retailer or a service business, so there is nobody to have written a review. Several competitors run testimonial sections; ours would have to be invented, and an honest absence beats a fabricated endorsement.

Scooter M., an enthusiast who is genuinely into this - reads the manuals, compiles the published specs and does the math. Not a cosmetologist, trichologist or dermatologist, and nothing here is medical advice. More on the about page.