Lash Lift Chemistry: Reduction, Setting and Timing

Course: Lash lift and brow lamination course from A to Z · Module 2 of 8

Doing a good lift takes more than memorising steps – you need to understand lash lift chemistry. Knowing what happens inside the hair at each stage lets you read a manufacturer’s instructions properly, adapt to different lash types and, above all, avoid over-processing. This module covers the reducing stage, the setting (neutralising) stage and why timing is everything.

Module objectives

Understand the basic structure of hair and the bonds that hold its shape.
Know what the reducing lotion does and which actives are used (thioglycolate, cysteamine and others).
Know what the setting or neutralising lotion does.
Understand why processing times depend on the manufacturer and the lash type.
Recognise what happens when each stage is too short or too long.

Lash structure: what we’re changing

Lashes, brows and scalp hair are all made mainly of keratin. In her review in the International Journal of Trichology (2015), dermatologist Maria Gavazzoni Dias describes an outer cuticle of overlapping, chemically resistant scales and a cortex that makes up most of the hair’s mass. The keratin chains are held in shape by several chemical forces: ionic bonds, hydrogen bonds, van der Waals forces and disulfide bonds.

Disulfide bonds – links between sulphur atoms in the amino acid cystine – are what make a lash’s shape stable. A mechanical lash curler only has a temporary effect (Healthline points out that the curl wears off in the shower). For a shape that lasts weeks, those disulfide bonds have to be broken, the hair repositioned, and the bonds re-formed in the new position. That’s exactly what any perm does, whether on hair, lashes or brows.

Stage 1: the reducing lotion

The first lotion – called “Step 1”, “Lift”, “Form 1” or “perm lotion” depending on the brand – contains a reducing agent that breaks the disulfide bonds. Put simply, each disulfide bond (R‑S‑S‑R) becomes two thiol groups (R‑SH). With the bonds open, the lash becomes pliable and takes on the shape of the silicone shield it’s been fixed to.

Gavazzoni Dias explains that alkaline solutions swell the fibre and open the cuticle scales, which lets the reducing agent penetrate. She also notes that the cuticle and the cell membrane complex (the “glue” between cells) are very vulnerable to chemical treatments, and that much of the damage caused by reducing products is down to misuse.

Common reducing agents

Active	What we know	Source
Ammonium thioglycolate / thioglycolic acid	The classic perm reducing agent. In the EU, in eyelash waving products: max 11% (as thioglycolic acid), pH 7–9.5, professional use only	Regulation (EU) 2015/1190; InLei Form 1 product page
Cysteamine hydrochloride	Found in some lash lift and lamination lotions. Some brands market it as gentler on skin	ReFocus Eye Health; Sugarlash Pro (manufacturer claim)
Other reducing agents (ammonium thiolactate, cysteine HCl, sodium sulphite)	Appear in combination in some commercial formulas	InLei Form 1 ingredient list published by a distributor

Be cautious about cysteamine claims. We couldn’t find independent studies comparing it with thioglycolate on lashes, so “gentler” or “skin-safe” should be treated as each brand’s marketing. What is documented is that all of these substances can cause burns or allergic reactions if they reach the surface of the eye or the skin (ReFocus Eye Health).

Stage 2: setting or neutralising

Once the lash has taken the shape of the shield, the bonds need to be “closed” again in that position. That’s the job of the second lotion (“Step 2”, “Fix”, “Lock”, “setting lotion” or “neutraliser”), which contains an oxidising agent. Perm literature names hydrogen peroxide and sodium bromate as the usual oxidants, and Gavazzoni Dias notes that thioglycolate must be oxidised (neutralised) with a hydrogen peroxide solution. InLei’s Fix 2, for example, lists hydrogen peroxide among its ingredients.

The oxidant rejoins the thiol groups as disulfide bonds – but now in the new position. That’s why it’s essential to remove the first lotion thoroughly before applying the second, and to respect the setting time: if setting is incomplete, the lash doesn’t properly “remember” its new shape.

Stage 3 (optional): conditioning

Many systems include a third conditioning step, such as InLei’s Fill 3, whose ingredients include hydrolysed keratin, panthenol and glycerin. This step doesn’t set the shape – its role is cosmetic and conditioning. Use it when and how the system’s manufacturer specifies. You’ll find complete systems and individual steps in our lamination category.

Lash lift chemistry, step by step

This is the chemical logic behind every lash lift. The full practical technique comes in Module 5.

Cleanse. Remove make-up, oil and residue so the lotion works evenly.
Shape. Fix the lashes onto the shield with glue or balm – this will be the final shape.
Reduce. Lotion 1 opens the disulfide bonds for the time the manufacturer specifies.
Remove lotion 1. Take it off completely to stop the reduction and avoid mixing it with the oxidant.
Oxidise. Lotion 2 re-forms the bonds in the new position.
Remove and condition. Take off lotion 2 and, if the system includes it, apply the conditioning step.

The California Board of Barbering and Cosmetology is explicit on this: remove and neutralise all lash lift and brow lamination product according to the manufacturer’s protocol.

Why timing matters so much

The reaction isn’t all-or-nothing: the longer the reducing agent works, the more bonds it breaks. That makes processing time the most delicate variable in the whole service. Under- and over-doing it have different consequences:

Situation	What happens
Under-processing	Too few bonds are opened and the lash doesn’t take the shape well: weak lift, or one that drops early
Over-processing	Dry, brittle lashes, over-curl or frizz and risk of breakage (Healthline, Cleveland Clinic)
Incomplete setting	Bonds don’t re-form properly and the shape doesn’t hold
Product on skin or eye	Irritation, burns or allergic reaction (ReFocus Eye Health, Healthline)

What the right time depends on

The specific system. Each manufacturer calibrates its formula (concentration, pH, texture) and sets its own times. There’s no universal timing.
The lash type. An InLei distributor sums up the rule: the stiffer and straighter the lashes, the longer the processing time; fine or already-curved lashes need less.
Chemical history. Recently treated lashes are more fragile. InLei, for instance, advises reducing times when redoing a lift, and waiting 24 hours to 7 days if the previous lift was done with another brand.
Product condition. Opened sachets lose effectiveness over time. InLei says to use its sachets within a month of opening; another brand (Sugarlash Pro) advises not keeping its sachets open for more than an hour. Once a product has weakened, timings stop being reliable.

Published timing examples (not interchangeable)

To show how much they vary, here are timings published by one manufacturer. They only apply to that product and may change between versions – always check the leaflet in your own kit.

System	Lotion 1 (according to the manufacturer)	Lotion 2 (according to the manufacturer)
InLei Lash Filler (product page)	5–10 min depending on lash strength	A further 5 min
InLei 25.9 Intro Kit (kit page)	6–12 min depending on lash strength	About half the lotion 1 time

Notice that two official pages from the same brand give different ranges for lotion 1 – and one expresses setting as a fixed time while the other expresses it as a proportion of the reducing time. Every other brand publishes its own timings too. Hence the golden rule of this course: timings come from the leaflet for the batch you’re using, never from a blog, a colleague or another brand. InLei also warns against combining products from different brands, as the result can’t be predicted.

Working with a lash lift also means having the right adhesive and accessories ready before you open any lotion – see our glue and liquids and accessories categories, and Module 3 for the full kit list.

Common mistakes

Leaving lotion 1 on “a bit longer, just in case”. It’s the fastest route to over-processing.
Applying lotion 2 without fully removing lotion 1. Reduction carries on and setting is uneven.
Mixing steps from different brands. Each setting lotion is formulated for its own reducer.
Using the same time for every client. Lash type and history change the response.
Using a sachet opened weeks ago. Past the manufacturer’s limit, the reaction is unpredictable.
Thinking the conditioner sets the curl. Lotion 2 sets; the conditioner conditions.

Module summary

A lash’s stable shape depends mainly on the disulfide bonds in keratin.
Lotion 1 (reducing) breaks them; thioglycolate is the most common active, cysteamine an alternative.
Lotion 2 (oxidising, often with hydrogen peroxide) re-forms them in the new position.
Timings depend on the manufacturer, lash type, chemical history and product condition.
Over-processing dries and weakens lashes; under-processing gives a lift that won’t hold.

Self-assessment

1. Which bonds must be broken for a lash lift to last for weeks?

The disulfide bonds in keratin. Mechanical curling only changes the shape temporarily.

2. What kind of chemical reaction does lotion 2 produce?

Oxidation: the oxidising agent (such as hydrogen peroxide) rejoins the thiol groups into disulfide bonds, setting the new shape.

3. Why can’t you use one kit’s timings with another kit?

Because each manufacturer calibrates its formula’s concentration, pH and texture and sets its own timings. Even one brand can publish different ranges for different products.

4. A client has thick, stiff, very straight lashes. What does that mean for the lotion 1 time?

As a rule, she’ll need a time towards the upper end of the manufacturer’s range – never beyond it.

Sources

Note: this module is for information only and does not replace hands-on training with a qualified trainer. The timings quoted are examples published by the manufacturer – always follow the instructions for the product you’re using.

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All the supplies for this course are available at Lash Canarias:

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