The Digital Perm

The thing that defines it: curliest when dry

Take one fact from this page and take this one. Every cold wave in this library is curliest when the hair is wet and relaxes a little as it dries. A digital perm does the opposite. Straight out of the shower it looks loose and close to straight; as the water leaves, the curl draws up and tightens.

A cold wave is curliest when wet. A digital perm is curliest when dry. Almost everything else about the service follows from that inversion.

The shape was set in the absence of water. On a cold wave the fibre is reduced, bent round a rod and rebuilt while soaking, so water is present when the new bonds form and is part of the shape the hair remembers. On a digital perm the hair is held on a warm rod while moisture is driven out of it, and the shape is fixed dry. Put the water back and the hair goes looking for the straighter configuration it can only reach when wet and heavy.

Which is why the commonest mismatch in the chair is the client who wants wash-and-go. A digital perm is a blow-dry perm. If you want hair at its best air-dried, a cold wave or a cysteamine wave is the right service.

Heat perming itself is old — Karl Nessler demonstrated a thermal machine perm in London in 1906, told at Nessler and the first perm. What is modern is the reason. Cold waves work beautifully on fine and medium European hair and frequently fail on thick, coarse, dense East Asian hair, where a large rod at room temperature gives a wave that has dropped inside a month. Japanese and Korean makers answered that in the late 1990s by putting the heat back, under electronic control.

Level of change

The teCsture Scale runs from 1, the tightest pattern, to 10, poker straight — one ladder, ten rungs. What a treatment does is move you a number of rungs. That distance is the job, and it is what the work should be priced on: the level of change, not the bottle.

On heavy, coarse, stubbornly straight hair this reaches rungs a cold perm cannot — and holds them for most of a year.

The order runs backwards from a cold perm

On a cold wave you wind first and apply lotion to hair already on the rods. On a digital perm you generally do the reverse: the lotion goes onto straight hair, the hair is rinsed and dried, and only then is it wound.

1. Consultation and elasticity test. The step with the power of veto. A wet strand is stretched and released. Hair that softens and does not spring back does not get this service at any setting.
2. Reduction, on straight hair. Twenty to forty minutes. A cream reducer opens some of the disulphide bonds before any shape is imposed, so the fibre is wound pliable rather than forced.
3. Rinse. The reducer comes off completely. Anything left in the hair is about to meet heat.
4. Dry thoroughly. The step people skim, and the one that decides whether the service is safe. Free moisture in a fibre about to be heated is the direct cause of bubble hair. The hair goes onto the rods dry, not damp.
5. Wind onto corded heated rods. Thirty to sixty minutes of slow work: each rod carries its own cable back to the processor, and a pad of felt or fabric goes between every rod and the scalp. Ends are papered — see end papers.
6. Heat, in cycles. Twenty to forty-five minutes. Not one continuous bake but short heating intervals separated by cooling intervals, so moisture leaves the fibre gradually.
7. Cool completely. Ten minutes, and it cannot be hurried — the shape is taken up as the hair cools on the rod. Unwinding warm loses much of the result.
8. Neutralise and finish. Peroxide or sodium bromate closes the bonds in the shape the heat has set. Then a rinse and a blow-dry, during which a competent stylist teaches you the finger-twist you will be repeating twice a week for months.

Three to four hours, and for part of it you are tethered to the machine by one cable per rod. Worth knowing before you book rather than at hour two.

Why the lotion is weaker than a cold wave’s

This surprises people, because a digital perm looks like the stronger service and lasts far longer. The lotion made for a heated-rod system is milder than the one that would go on the same head at room temperature — thioglycolate, cysteamine or a hybrid, usually a cream, and formulated to do less.

The arithmetic is simple. Reduction and heat are two ways of getting the same job done, and the machine supplies one. If the heat reshapes part of the structure, the chemistry only has to open the rest.

It also explains why borderline hair does not become eligible by choosing this service. Heat is not a gentler substitute for chemistry; it is an extra load on the same fibre. The elasticity test applies at least as strictly as on a cold wave, and more strictly on porous hair, which takes up both lotion and heat faster than anyone expects.

Why there is no temperature on this page

Search for this service and you will be handed numbers within ten seconds. Trade material carries several ranges, they do not agree with each other, and this library publishes none of them. That is a decision, so here is the reasoning.

What can honestly be said is that the rods are warm, not iron-hot. A digital perm is nothing like running a straightener over dry hair, and a machine that felt like one would be faulty. The heat arrives in cycles, and the operator sets it to the hair in the chair. Ask your stylist what machine they run, what lotion it is matched to, and why they chose that cycle.

Bubble hair, fishhooks and burns

Bubble hair

The failure specific to heat, and the reason the drying step matters. Water sits inside the cortex, and under heat it becomes steam. Steam takes far more space than the water it came from, and if it is generated faster than it can leave it forces its way out through the shaft, blowing cavities along the fibre. Under a microscope it looks exactly like its name. The lengths are hollow, they part under very little load, and there is no treatment — no protein, no bond builder, no conditioner. The hair is cut off where the cavities begin.

This is why the hair is dried properly before winding, and why the heat runs in cycles with cooling intervals rather than continuously.

Fishhook ends

A tip that folds back on itself during the wind is set at that angle, and heat sets it harder than a cold wave does. The result is a jagged right-angle crimp at the end of every affected curl, which reads as frizz and cannot be conditioned out. The defence costs a fraction of a penny: an end paper pulled past the longest tip in the section, and even tension. See end papers.

Scalp burns

The rods are warm and the scalp is skin. A pad of felt or fabric goes between every rod and the head — not most rods, every rod — and pads that shift during the wind are why burns happen. If a rod feels hot on your scalp, say so at once.

Who it is for, and who it is refused

Not for fine or fragile hair. Heat plus tension on a fibre with nothing to spare gives dull, scorched lengths that part under low load. Fine hair wanting movement is better served by a cold wave on large rods or by a gentler chemistry such as a cysteine perm.

Over tint: possible on a healthy single-process colour, with a milder cream, a shorter cycle and a strand test first. Over a hydroxide relaxer: never, in either direction — see perm versus relaxer. Over Japanese straightening: related chemistry, technically possible, but only on virgin regrowth and only by someone who does it often. Pregnancy: postpone, and note that three hours tethered to a heated machine is its own argument.

How long it lasts, and what it asks of you

Six to nine months is the honest figure, at the longer end on coarse hair and the shorter end on anything finer. Longer claims circulate freely, and on very thick hair a year does happen. It is not what most people get, and a salon promising it is promising the best case.

What ends it is usually growth, not the curl relaxing. Hair grows about half an inch, a little over a centimetre, a month, so by month six there is a straight band at the root as wide as your palm, and that band is what reads as grown out. The fix is a root reapplication, not a full head.

The blow-dry is the style

Rough-dry the roots, then take large sections, twist each away from your face around your fingers, and direct the airflow down the section as it dries. You are recreating the tension of the hot rod, and it is the difference between the perm you paid for and a slight bend. Scrunching, right for a cold wave, does little here.

Water, sun and the first three days

London water is hard. One small advantage here: the heat leaves the cuticle flatter and better sealed than a cold wave does, so a digital perm resists mineral dulling slightly. Slightly. A chelating wash roughly monthly still applies — see curl memory and water. The shape holds up unusually well in humidity, which is much of the appeal, but sun and salt dry the lengths, so the ends want a mask before swimming rather than after.

Seventy-two hours. Neutralising reforms the bonds but it does not finish the job on the spot — oxidation carries on in air after you leave and the fibre goes on hardening for about three days. In that window what you press into the hair tends to stay: no tight ties, no clips, no hard brushing, and go gently with heat. For washing, follow the instruction for the product actually used on your head.

Questions