The Laser-IPL Guys · Student Resource Series
Laser/IPL
Hair Removal
Quick-Reference Booklet — 2nd Edition
Overview & Fundamentals
Science & Biology
Skin Cooling
Hair Growth Cycles
Choosing Settings
Clinical Protocols
Technology: Lasers & IPLs
The 7 Core Principles
- Hair melanin (eumelanin / pheomelanin) is the primary target chromophore.
- Correct wavelength choice forces preferential absorption in hair over surrounding tissue.
- Absorbed light energy converts to heat — raising follicle temperature.
- Epidermal melanin also heats up; darker skin = greater epidermal risk.
- Ideal scenario: dark hair + pale skin — maximum contrast.
- As skin darkens, the hair/skin temperature differential narrows.
- Very dark skin may preclude treatment due to epidermal overheating risk.
Hair Colour & Melanin Type
| Hair Colour | Melanin Type | Treatability |
|---|
| Black / dark brown | Eumelanin (high) | Excellent |
| Light brown | Eumelanin (mod) | Good |
| Red / auburn | Pheomelanin | Variable |
| Blonde / grey / white | Minimal | Poor / none |
Key Treatment Parameters
- Wavelength — must be absorbed by melanin, not water
- Fluence — energy delivered per unit area (J/cm²)
- Pulsewidth — duration of each light pulse (ms)
- Spot size — affects penetration depth
- Skin cooling — pre-, during- and post-treatment essential
- Repetition rate — pulses per second (Hz) for SHR mode
Hirsutism vs Hypertrichosis
- Hirsutism — androgen-driven excess hair in female hormone-sensitive sites
- Hypertrichosis — generalised excess hair, not hormone-dependent
- Both can be treated with laser/IPL but underlying cause should be investigated
What Cannot Be Treated?
- White, grey, or very blonde hair (no melanin target)
- Fitzpatrick VI skin (very high epidermal overheating risk)
- Tanned skin (temporary contraindication)
- Active skin conditions over the treatment area
- Tattoos, moles, or darkly pigmented lesions in the beam path
Clinical language reminder: When speaking with clients, use terms like "significant reduction" or "long-term hair reduction" rather than "permanent hair removal." The distinction matters legally and ethically.
Selective Photothermolysis (SP)
- Target must absorb wavelength more than surrounding tissue
- Pulsewidth ≤ Thermal Relaxation Time (TRT) of target
- Sufficient fluence to reach damaging temperature
Anderson & Parrish's foundational principle underlies all light-based treatments.
Thermal Relaxation Time (TRT)
| Structure | TRT (approx.) |
|---|
| Hair shaft (fine) | 15–40 ms |
| Hair shaft (thick) | 40–100 ms |
| Hair bulb / follicle | 50–100+ ms |
| Epidermis | 3–10 ms |
Pulsewidth should approximate the TRT of the follicle — not just the shaft.
Penetration Depth — Key Factors
- Longer wavelength → deeper penetration
- Larger spot size → deeper effective penetration (less scatter divergence)
- Higher fluence → reaches deeper follicles, but increases epidermal risk
- Back-scattering can increase fluence up to ~1.4 mm below the surface
Epidermal Melanin & Skin Risk
- Melanin in epidermis ranges from ~2% (Fitzpatrick I) to >43% (Fitzpatrick VI) by volume
- Epidermal melanin absorbs light before it reaches the follicle — energy is "lost"
- Higher skin melanin → higher epidermal temperature → higher burn risk
- This is why skin cooling is non-negotiable
KILL
Fluence is sufficient. Follicle temperature reaches denaturation. Permanent destruction.
STUN
Fluence is sub-threshold. Follicle is temporarily impaired but recovers — fine/pale regrowth.
NULL
Fluence is too low. No meaningful thermal effect. Hair regrows normally.
The Kill–Stun–Null framework applies to all light-based treatments, not just hair removal.
Eumelanin vs Pheomelanin — Absorption
- Eumelanin absorbs strongly across 600–1100 nm — ideal target
- Pheomelanin absorbs mainly in UV-blue range; poor NIR target
- Red/ginger hair has high pheomelanin — explain to clients why results may vary
Pulsewidth influences temperature and cell damage independently of fluence. Too short a pulse at high fluence risks explosive vaporisation; too long a pulse at borderline fluence allows heat dissipation before damage occurs. Both dimensions matter.
Why Cooling is Critical
- We are deliberately inducing a controlled "burn" — targeting follicles while protecting dermis and epidermis
- Cooling extracts excess heat from the epidermis before it propagates down to non-target tissue
- Effective cooling allows use of higher, more effective fluences safely
- Proper cooling can eliminate pain almost entirely
Cooling Timing: Before · During · After
- Pre-cooling: Chills epidermis before pulse — most protective phase
- Contact cooling (during): Continuously removes heat at the surface during treatment
- Post-cooling: Ice pack for up to 10 minutes after session removes residual heat and minimises risk of delayed damage
Comparing Cooling Methods
| Method | Efficacy | Notes |
|---|
| Ice packs / contact ice | ⭐⭐⭐⭐⭐ | Best — direct conduction |
| Cryogen spray | ⭐⭐⭐⭐ | Effective, requires timing |
| Air cooling (Zimmer) | ⭐⭐⭐ | Good adjunct, not primary |
| Equipment "cold tip" | ⭐ | Keeps components cool — not designed to cool skin adequately |
The "Pain-Free" Principle
- With correct ice cooling applied for several minutes pre-treatment, very high fluences can be used with minimal sensation
- Reassure clients: lack of pain does not mean the treatment is ineffective
- Pain ≠ efficacy
Over-Cooling: Is it Possible?
Virtually impossible to cool the skin too much with contact ice. Cooling predominantly affects the epidermis; deeper follicles retain enough heat for the treatment to work even with aggressive surface cooling.
Cooling Limitations
- Very dark skin (Fitzpatrick V–VI): may generate temperatures too high to be compensated by any cooling method
- In these cases, reduce fluence or consider a longer wavelength (Nd:YAG 1064 nm)
- Never rely solely on a machine's built-in cold contact window
The rule: Cool before, during, and after every photothermal treatment. The goal is to maintain epidermal temperature below the damage threshold (~45–50°C sustained) while raising follicle temperature above the denaturation threshold (~70°C).
Research by Murphy & Torstensson has shown that with adequate contact ice cooling, fluences that would normally produce significant pain and risk can be delivered with near-zero sensation. This changes the clinical calculus on what "safe" fluence levels look like.
The Three Growth Phases
| Phase | Activity | Treatability |
|---|
| Anagen | Active growth; melanin-rich shaft connected to bulb | Excellent — primary target |
| Catagen | Transition; follicle shrinking | Moderate |
| Telogen | Resting; no attachment to bulb | Poor — no effective target |
Anagen Percentage by Body Site
| Body Site | Anagen % | Cycle (approx.) |
|---|
| Scalp | ~85% | 2–6 years |
| Upper lip | ~65% | 4–8 weeks |
| Axilla | ~30% | 4 months |
| Legs | ~20% | 6 months |
| Back | ~15–20% | 6–12 months |
| Bikini line | ~30% | 3–4 months |
These proportions explain why multiple sessions are always required — only anagen hairs respond effectively to each treatment.
The Critical Timing Principle
The longer the interval between sessions, the fewer treatments overall are needed.
Waiting allows more hairs to enter anagen — meaning each subsequent session treats a larger proportion of follicles effectively.
Suggested Treatment Intervals by Site
| Body Site | Recommended Interval |
|---|
| Face (upper lip, chin) | 4–8 weeks |
| Underarms | 6–8 weeks |
| Bikini / Brazilian | 6–10 weeks |
| Legs | 8–16 weeks |
| Back / chest | 8–16 weeks |
Regrowth Patterns
- "Regrowth" after treatment is usually anagen hairs that were in telogen during treatment — not treated hairs regrowing
- Stunned (sub-threshold) hairs often regrow finer and lighter — this is expected and manageable with correct fluence
- Dormant follicles may activate post-treatment — explain this to clients as a possible complication on some sites
Hair shaft/follicle size matters: Thick, dark hairs in deep follicles require more fluence than fine, light hairs. Thicker hairs contain more melanin and therefore absorb more energy — but their follicles may also sit deeper, requiring the light to penetrate further.
Clinical Endpoints to Look For
- Perifollicular erythema — redness around follicle openings (positive sign)
- Perifollicular oedema — slight swelling around follicles (good indicator)
- Singed hair smell — indicator of sufficient heating in stamping mode
- No excessive erythema — widespread redness = too much epidermal heating
- No blistering/blanching — signs of over-treatment requiring immediate cooling
Approximate Threshold Fluences (Starting Points)
| Device Type | Fitzpatrick I–II | Fitzpatrick III–IV |
|---|
| IPL (550–1200 nm) | 10–15 J/cm² | 8–12 J/cm² |
| Diode 808/810 nm | 15–25 J/cm² | 10–18 J/cm² |
| Alexandrite 755 nm | 12–20 J/cm² | 8–14 J/cm² |
| Nd:YAG 1064 nm | 20–35 J/cm² | 18–30 J/cm² |
Always perform a test patch before full treatment. Adjust based on observed clinical endpoints and skin response.
Recommended Starting Fluences by Body Site
| Site | Relative Fluence |
|---|
| Face / upper lip | Lower (thinner skin, more sensitive) |
| Underarms / bikini | Moderate |
| Legs / arms | Moderate–higher |
| Back / chest | Higher (thicker skin, deeper follicles) |
Why Finer/Lighter Hairs Appear After Treatment
This is the hallmark of the Stun Zone — follicles that were damaged but not destroyed regenerate, producing reduced-calibre, less-pigmented hair. To progress these to the Kill Zone, increase fluence on subsequent treatments and ensure adequate cooling.
Test Patches — Why They Matter
- Always test a small area 24–48 hours before full treatment
- Assess skin reaction: erythema, oedema, no blistering
- Review at 48h and again at 1 week for delayed adverse reactions
- Especially important for Fitzpatrick III+ skin
- Document test patch parameters for reproducibility
Pain as a Guide
- Aim for a pain level of 3–5 out of 10 with standard cooling
- Zero pain with good ice cooling is acceptable and effective
- "No pain, no gain" is not true for hair removal — adequate cooling can make treatments pain-free without sacrificing efficacy
- Severe pain may indicate insufficient cooling or excessive fluence
Increasing fluence incrementally while monitoring clinical endpoints gives you more information than jumping to a high fluence. Begin conservatively, observe, then adjust upward — particularly on a new client, new body site, or new device.
Hair Removal Devices: Wavelengths & Fit
| Device | Wavelength | Skin Type |
|---|
| Diode laser | 808/810/940 nm | I–IV (some to V) |
| Alexandrite laser | 755 nm | I–III |
| Nd:YAG laser | 1064 nm | I–VI (darkest skin) |
| Ruby laser | 694 nm | I–II only |
| IPL system | 515–1200 nm (filtered) | I–IV (cut-off filter) |
| Triple diode | 755+808+1064 nm | I–V |
IPL Filtering — How It Works
- Flashlamp produces broadband light from UV to ~1200 nm
- Cut-off filters remove short wavelengths (UV, blue, green) to protect epidermis
- Common filters: 550, 640, 695, 755 nm cut-offs
- Darker skin types require a higher cut-off filter to reduce epidermal absorption
- Light energy is distributed across the remaining spectrum — not all equally effective for hair
Diode Laser: Stamping vs SHR
- Stamping: single high-fluence pulse; more effective for coarse hair; higher pain potential
- SHR/in-motion: multiple low-fluence passes; lower pain; effective across a wider range of skin types
- Neither is universally superior — depends on hair type, skin type, and device capability
Laser vs IPL — Key Differences
| Feature | Laser | IPL |
|---|
| Wavelength | Single (monochromatic) | Broadband (filtered) |
| Coherence | Coherent, collimated | Non-coherent |
| Penetration | More predictable | Variable by filter |
| Cost | Generally higher | Generally lower |
| Versatility | Limited to design spec | Multiple indications via filters |
| Clinical results | Comparable with correct use | Comparable with correct use |
With appropriate settings and technique, IPLs and lasers achieve comparable hair removal outcomes. Device type is less important than operator knowledge.
Common Myths — Debunked
- "IPLs are always inferior to lasers" — False. Results depend on settings and technique.
- "More pain = more effective" — False. Adequate cooling removes pain without reducing efficacy.
- "One treatment is enough" — False. Multiple sessions always needed due to hair cycle.
- "SHR machines need a special laser" — False. SHR is a technique, not a technology.
- "The cold tip on my machine cools the skin" — False. Machine cold tips cool components, not the dermis.
The key insight: With any device, the limiting factor for effective hair removal is almost always insufficient fluence reaching the follicle — due to under-powered settings, inadequate skin cooling, or poor technique. Knowing the physics allows you to address all three.
Chapter 3, Ed. 2.0 · Laser/IPL Hair Removal · Murphy & Torstensson · © The Laser-IPL Guys 2025
Free student resource — dermalasetraining.com