CORE PRINCIPLE

Selective photothermolysis:
Laser wavelength is chosen to be preferentially absorbed by the tattoo pigment while sparing surrounding skin.

• Short pulse duration (nanosecond/picosecond) → photoacoustic fragmentation of pigment

• Fragments cleared by macrophages/lymphatics

LASER SELECTION BY INK COLOR

Rule: A laser removes colors opposite to its wavelength on the color spectrum (complementary absorption).

Black pigment

• Best treated

• Absorbs all wavelengths

• Lasers:

  • Q-switched Nd:YAG 1064 nm (first-line)

  • Ruby 694 nm

  • Alexandrite 755 nm

Blue / dark purple

• Alexandrite 755 nm

• Ruby 694 nm

Red / orange

• Q-switched Nd:YAG 532 nm

• (Strong absorption by red pigments)

Green (difficult color)

• Alexandrite 755 nm (best option)

• Ruby 694 nm (less effective)

Yellow

• Very resistant

• Poor absorption of available wavelengths

White / flesh-colored pigments

• Contain titanium dioxide or zinc oxide

• Poor response to lasers

• Risk of paradoxical darkening (very high-yield)

PRACTICAL LASER SUMMARY

• 1064 nm (Nd:YAG): black, dark blue; safest for darker skin

• 532 nm (Nd:YAG frequency-doubled): red, orange

• 755 nm (Alexandrite): green, blue

• 694 nm (Ruby): blue, green (less used now)

FACTORS AFFECTING RESPONSE

• Ink color (most important)

• Depth of pigment

• Professional vs amateur tattoo (professional = deeper, harder)

• Skin type (Fitzpatrick type)

• Age of tattoo (older = easier)

• Immune clearance efficiency

COMPLICATIONS

1. PARADOXICAL DARKENING (VERY HIGH-YIELD)

Definition

Unexpected darkening of tattoo pigment after laser treatment

Mechanism

• Reduction of metal oxides:

  • Ferric oxide (Fe³⁺ → Fe²⁺) → turns black

  • Titanium dioxide reduction

• Laser energy alters chemical structure → darker pigment forms

High-risk pigments

• White

• Flesh-colored

• Cosmetic tattoos (eyebrows, lip liner)

Clinical implication

• Tattoo becomes darker instead of fading

• May require different laser wavelength afterward

Exam pearl:
Most commonly seen with cosmetic tattoos

2. TEXTURAL CHANGES

Types

• Scarring (atrophic or hypertrophic)

• Skin atrophy

• Surface irregularity

Mechanism

• Excess thermal injury to dermis

• High fluence or improper technique

• Repeated treatments causing collagen damage

Risk factors

• Aggressive settings

• Darker skin types

• Infection or poor wound care

OTHER IMPORTANT COMPLICATIONS

Pigmentary changes

• Hypopigmentation (melanocyte damage; common with 1064 nm in dark skin)

• Hyperpigmentation (post-inflammatory; more common in darker skin)

Incomplete removal

• Especially green, yellow, white pigments

Allergic reactions

• Laser fragmentation → release of antigenic pigment → hypersensitivity

Infection (rare)

• PREVENTION STRATEGIES Choose correct wavelength for pigment color

• Use appropriate fluence (avoid overtreatment)

• Space sessions adequately

• Sun protection (prevent PIH)

• Test spot in cosmetic tattoos (to detect paradoxical darkening)

CLINICAL APPROACH

1. Identify tattoo colors

2. Select appropriate laser wavelength

3. Consider skin type (adjust settings)

4. Warn patient about:

   • Multiple sessions required

   • Risk of incomplete removal

   • Possibility of paradoxical darkening

EXAM-FOCUSED INSIGHTS

• Black ink = easiest to remove

• Green & yellow = most difficult

• White pigment = risk of paradoxical darkening

• Nd:YAG 1064 nm = safest for darker skin

• Tattoo removal is mechanical fragmentation + immune clearance

MUST-KNOW QUESTIONS

1. Principle behind laser tattoo removal?
   Selective photothermolysis

2. Best laser for black ink?
   Q-switched Nd:YAG 1064 nm

3. Best laser for red pigment?
   532 nm Nd:YAG

4. Most difficult tattoo color to remove?
   Yellow (and green)

5. Which pigment is easiest to remove?
   Black

6. What is paradoxical darkening?
   Tattoo becomes darker after laser treatment

7. Which tattoos are most prone to paradoxical darkening?
   Cosmetic tattoos (white/flesh-colored)

8. Mechanism of paradoxical darkening?
   Reduction of metal oxides (e.g., ferric oxide → ferrous oxide)

9. Main cause of textural changes?
   Excess thermal injury to dermis

10. Most common pigmentary complication?
    Hypopigmentation or hyperpigmentation

11. Why are multiple sessions needed?
    Gradual pigment fragmentation and immune clearance

12. Safest laser for darker skin types?
    Nd:YAG 1064 nm