What is dermatology?
Dermatology is the branch of medicine that studies and treats the skin, hair and nails. The word comes from Greek: derma (skin) + logia (study). A doctor who specialises in it is a dermatologist.
Dermatologists treat everything from acne, eczema and psoriasis to hair loss, infections and skin cancer — and they also perform procedures like laser treatments, peels and minor surgery.
Think of it like this: your skin is a smart raincoat. It keeps water in, germs out, controls temperature, senses touch — and even makes vitamin D from sunlight.
Meet your skin: three layers
To understand lasers, you first need to know what they are aiming at. Skin is built like a three-layer cake:
The protective shield. Contains melanocytes that make melanin — the pigment that gives skin its colour and causes tans, freckles and dark spots.
The “engine room”. Full of collagen (for firmness), elastin (for stretch), blood vessels, nerves, sweat glands and hair roots. Most laser targets live here.
A cushion of fat that stores energy, keeps you warm and connects skin to muscle.
What exactly is a laser?
“LASER” is actually an acronym:
In simple words: a laser is a device that makes a very pure, focused and powerful beam of light. Inside, atoms are “excited” with energy, and when they calm down they release light. Mirrors bounce this light back and forth, multiplying it, until a strong beam escapes.
Torch light vs laser light
Ordinary light (torch, bulb)
- Many colours mixed
- Waves out of step
- Spreads out in all directions
Laser light
- Monochromatic — one single colour (wavelength)
- Coherent — waves march in step
- Collimated — travels in a tight, straight beam
These three properties let doctors aim light energy at one exact target in the skin — something ordinary light can’t do.
Wavelength = the laser’s “colour”
Every laser produces one wavelength, measured in nanometres (nm). Some are visible (green, red), but many medical lasers use invisible infrared or ultraviolet light. The wavelength decides what the laser hits and how deep it goes.
A short history
- 1917
The idea
Albert Einstein describes “stimulated emission” — the physics that makes lasers possible.
- 1960
First laser
Theodore Maiman builds the first working laser using a ruby crystal (694 nm red light).
- 1963
Lasers meet skin
Dermatologist Dr. Leon Goldman begins studying lasers on skin — he is often called the “father of laser medicine”.
- 1983
The big breakthrough
Anderson & Parrish publish selective photothermolysis: how to heat only a chosen target without harming nearby skin.
- 2004
Fractional lasers
Fractional photothermolysis treats tiny columns of skin at a time, so healing becomes much faster.
- 2010s
Picosecond era
Ultra-short picosecond pulses arrive for tattoos and pigment — shattering particles with less heat.
How lasers treat skin
Here’s the big idea, called selective photothermolysis. Break the word apart: selective (choosing) + photo (light) + thermo (heat) + lysis (destroy). So: using light to heat and destroy only a chosen target.
Everyday example: on a sunny day, a black T-shirt gets much hotter than a white one. Dark colours absorb light and turn it into heat. Lasers use the same trick — dark hair roots or pigment absorb the light and heat up, while the lighter skin around them stays cooler.
Step 1 — Find the target (chromophore)
The thing in the skin that absorbs the laser light is called a chromophore (“colour-carrier”). There are four main ones. Tap each to learn more:
- Found in
- Hair roots, freckles, dark spots
- Absorbs
- 532 – 1064 nm
- Why it works
- Brown/black pigment absorbs a wide range of visible and near-infrared light.
- Found in
- Blood inside tiny vessels
- Absorbs
- 532, 585–595, 1064 nm
- Why it works
- Red blood absorbs green–yellow light strongly, so vessels heat up and close.
- Found in
- Every skin cell (≈ 70% water)
- Absorbs
- 2940 & 10,600 nm
- Why it works
- Far-infrared light is soaked up by water, so the laser can gently vaporise thin layers of skin.
- Found in
- Ink particles in the dermis
- Absorbs
- 532, 755, 1064 nm
- Why it works
- Each ink colour absorbs a different wavelength — that is why coloured tattoos need several lasers.
Step 2 — The three “golden rules”
Right wavelength
Pick a colour of light the target absorbs strongly — and that reaches the right depth.
Right pulse duration
Flash the light shorter than the time the target takes to cool down (its thermal relaxation time), so heat stays trapped in the target.
Right energy
Deliver just enough energy (fluence, in J/cm²) to affect the target — but not the skin around it.
Step 3 — What the light does
Target is heated and damaged — e.g. hair roots, blood vessels.
Ultra-short pulses shatter particles — e.g. tattoo ink, pigment.
Water in cells boils away thin layers — e.g. CO₂ resurfacing.
Light triggers a reaction in cells — e.g. excimer for vitiligo.
Finally, the body’s own healing does the rest: it clears away the damaged bits and builds fresh collagen. That’s why results often keep improving for weeks after a session.
Types of lasers
Lasers are often grouped by how much they affect the skin’s surface:
Ablative
Removes the top layer. Strong results, 1–2 weeks healing. e.g. CO₂, Er:YAG
Non-ablative
Heats below the surface, skin stays intact. Little or no downtime. e.g. Nd:YAG, diode
Fractional
Treats tiny columns, leaves healthy skin between them. Faster healing. e.g. fractional CO₂
Common skin lasers at a glance
| Laser | Wavelength (nm) | Main target | Typical uses |
|---|---|---|---|
| Ruby | 694 | Melanin | Pigment, older tattoo removal |
| Alexandrite | 755 | Melanin | Hair removal (fair skin), pigment |
| Diode | 800–810 | Melanin | Hair removal |
| Nd:YAG | 1064 | Melanin, blood | Hair removal on darker skin, veins, tattoos |
| KTP / Pulsed dye | 532 / 585–595 | Haemoglobin | Redness, rosacea, birthmarks |
| Er:YAG | 2940 | Water | Light resurfacing, fine lines |
| CO₂ | 10,600 | Water | Deep resurfacing, scars, wrinkles |
| Excimer | 308 | Immune cells (UVB) | Vitiligo, psoriasis |
IPL (Intense Pulsed Light) is often used alongside lasers, but it is not a laser — it uses a broad band of many wavelengths with a filter.
Where lasers are used in dermatology
Hair reduction
Heats the hair root so it stops growing thick hair.
Pigmentation
Breaks up extra melanin in sun spots, freckles and melasma.
Resurfacing
Removes damaged top layers and triggers fresh collagen.
Acne scars
Remodels pitted scars by rebuilding collagen underneath.
Blood vessels
Closes tiny visible vessels, calming redness and rosacea.
Tattoo removal
Shatters ink into tiny bits the body can clear away.
Vitiligo & psoriasis
Targeted UV light (excimer) calms or re-pigments patches.
Skin rejuvenation
Gentle heat boosts collagen for firmer, brighter skin.
Want to go deeper? Each application has its own topic page with the science, treatment steps and risks.
Safety & skin types
Medical lasers are powerful (most are Class 4 — the highest safety class), so they must be used by trained professionals.
The Fitzpatrick skin types
Because melanin absorbs laser light, darker skin can absorb energy meant for the target. Doctors use the Fitzpatrick scale to choose safer settings:
Good practice
- Special eye goggles for everyone in the room
- A patch test before full treatment
- Skin cooling during treatment
- Sun protection before and after
Possible side effects
- Temporary redness and swelling
- Darker or lighter patches (pigment change)
- Blisters or burns if settings are wrong
- Rarely, scarring
Glossary of key words
- Ablative
- A laser that removes (vaporises) the top layer of skin. More downtime, stronger results.
- Non-ablative
- A laser that heats tissue under the surface without removing skin. Little or no downtime.
- Chromophore
- The “target” in skin that absorbs laser light — e.g. melanin, haemoglobin, water or ink.
- Collagen
- A protein that gives skin strength and firmness. Many lasers work by making the body produce more.
- Dermis
- The thick middle layer of skin with collagen, blood vessels, nerves and hair roots.
- Epidermis
- The thin outermost layer of skin that acts as a protective barrier.
- Fitzpatrick scale
- A scale from I (very fair, always burns) to VI (deeply pigmented, never burns) used to choose safe laser settings.
- Fluence
- How much energy is delivered to one area of skin, measured in joules per cm² (J/cm²).
- Fractional laser
- A laser that treats thousands of tiny dots/columns and leaves healthy skin in between, so healing is faster.
- Melanin
- The natural pigment that colours skin, hair and eyes.
- Monochromatic
- Light of a single wavelength (a single colour). Laser light is monochromatic.
- Nanometre (nm)
- One-billionth of a metre. Laser wavelengths are measured in nanometres.
- Picosecond
- One-trillionth of a second. Picosecond lasers fire extremely short pulses.
- Pulse duration
- How long each flash of laser light lasts.
- Selective photothermolysis
- The key principle: using the right wavelength, pulse length and energy to heat only the target.
- Thermal relaxation time
- The time a target takes to lose half its heat. Pulses shorter than this keep heat from spreading.
- Wavelength
- The “colour” of light, measured in nm. It decides what the laser targets and how deep it goes.
No matching terms.
Test yourself
Six quick questions to check what you’ve learned.
Key takeaways
- Dermatology is the medicine of skin, hair and nails.
- Skin has three layers — most laser targets are in the dermis.
- A laser is pure, single-wavelength, focused light.
- Lasers work by heating only a chosen target (selective photothermolysis).
- Wavelength, pulse duration and energy must all be right.
- Skin type matters — safe settings protect darker skin.
This guide is for general education only and is not medical advice. Always consult a qualified dermatologist about your own skin.