Chemical Processing Time Reference
Accurate timing is critical in chemical hair services. Under-processing leads to incomplete results; over-processing causes damage, breakage and scalp irritation. This reference provides standard processing times for the most common chemical services, adjusted for hair type and condition. Always follow the specific manufacturer's instructions and monitor the hair throughout processing.
Permanent Colour
| Application type | Virgin hair | Regrowth | Porous / damaged | Resistant / grey |
|---|---|---|---|---|
| Full head (same level) | 30–35 min | 30–35 min | 20–25 min | 35–45 min |
| Full head (1–2 levels lift) | 35–45 min | 35–40 min | 25–30 min | 40–45 min |
| Going darker (depositing) | 25–30 min | 25–30 min | 15–20 min | 30–35 min |
Semi & Demi-Permanent Colour
| Type | Processing time | Heat required | Notes |
|---|---|---|---|
| Semi-permanent (deposit only) | 15–20 min | No | No developer; coats the cuticle; lasts 6–8 washes |
| Demi-permanent | 20–30 min | No | Low-volume developer; lasts 20–28 washes |
| Colour gloss / glaze | 10–20 min | No | Quick refresh and shine; minimal commitment |
Bleach / Lightener
| Application | Fine / porous hair | Medium texture | Coarse / resistant | Max. time |
|---|---|---|---|---|
| On-scalp (with 20 vol) | 20–30 min | 30–40 min | 35–45 min | 45 min max |
| In foils (with 30 vol) | 20–25 min | 25–35 min | 30–45 min | 50 min max |
| Open-air balayage | 20–30 min | 30–45 min | 35–50 min | 50 min max |
| Toner (post-bleach) | 5–10 min | 10–15 min | 15–20 min | 20 min max |
Never exceed the manufacturer's maximum processing time. Check every 5–10 minutes and remove bleach as soon as the desired level is reached.
Perms, Relaxers & Treatments
| Service | Fine hair | Medium hair | Coarse hair | Notes |
|---|---|---|---|---|
| Acid perm | 10–15 min | 15–20 min | 20–25 min | Gentler; check curl development every 5 min |
| Alkaline perm | 5–10 min | 10–15 min | 15–20 min | Stronger; shorter processing, tighter curl |
| Neutraliser (perm) | 5–10 min (all types) | Apply after rinsing perm lotion; do not skip | ||
| Chemical relaxer | 8–12 min | 12–18 min | 15–20 min | Smooth test every 3–5 min; max 20 min |
| Keratin treatment | 30–90 min flat-iron time (varies by brand) | Total service time 2–3 hours including application | ||
Chemical Services Calculators
Use our free tools for precise timing and formulation:
- Processing Time Calculator — get recommended processing times based on hair type
- Perm Rod Calculator — work out rod sizes and quantities needed
All times are guidelines only. Always follow the specific manufacturer's instructions, perform a strand test, and monitor the hair throughout processing. Hair that has been previously chemically treated will process differently to virgin hair. When in doubt, err on the side of shorter processing times.