Underarm Laser Hair Removal: Why Results Vary So Much Between Sessions

Underarm Laser Hair Removal: Why Results Vary So Much Between Sessions

As summer approaches, my clinic starts filling up fast —

patients with sleeveless outfit plans marked in their calendars,

and wedding dress fittings on the horizon.

"I've completed all 6 sessions,

so why does my underarm still look dark?"

I hear this all the time.

Today, I want to walk you through

exactly why that happens — step by step.

Underarm Laser Hair Removal — They're Not All the Same Laser

Laser hair removal works by targeting melanin in the hair follicle, converting light energy into heat to destroy the hair root.

Most people already know that part.

But what many don't realize is that under the umbrella of "laser hair removal,"

there are actually several different devices operating on different wavelengths.

The main ones are Alexandrite (755nm),

Diode (810nm),

and Nd:YAG (1064nm) —

and that number directly determines

how deep the light penetrates into the skin.

755nm has high melanin absorption, making it effective for shallower hair roots,

while 1064nm has lower absorption but reaches significantly deeper tissue.

This difference is what actually

separates results depending on the treatment area.

Same 6 Sessions — Why Does One Person Come Out Clean While Another Still Has Hair?

That might be hard to visualize from text alone — but a real case makes it crystal clear.

Last week, a 24-year-old woman came in

just to accompany her friend to a consultation.

The original appointment was her friend's leg hair removal consultation —

she was just along for the ride.

But as the conversation went on,

she opened up: "Actually, I had 8 sessions done somewhere else,

and the inner line of my underarm still hasn't cleared up."

By the end, she was more engaged than her friend.

When I reviewed her history,

it turned out every session had been done with a single 755nm Alexandrite wavelength.

Underarm hair roots sit at an average depth of 3–4mm.

That's deeper than facial vellus hair (around 1mm),

but shallower than coarse thigh hair (5–7mm) — truly a mid-range depth.

755nm can technically reach that depth.

But for the inner line and deeper, coarser follicles,

a significant portion of the 755nm energy gets absorbed by the epidermis

before it ever reaches the root.

This is the core point of today's post.

When we use the GentleMax Pro Plus to deliver

both 755nm and 1064nm together,

we consistently see hair reduction rates per session

run about 15–20% higher compared to single-wavelength approaches.

The 1064nm reaches deeper follicles,

while the 755nm handles the ones closer to the surface.

The patient I mentioned came back for 3 more dual-wavelength sessions,

and the inner line cleared up completely.

Why Does the Recommended Number of Sessions Differ by Body Area?

Seeing this laid out visually makes it much clearer.

Each area has different follicle depths and hair growth cycles,

which is why the number of sessions needed varies.

One important variable worth highlighting here:

if you're getting laser hair removal in the summer, UV exposure must be factored in.

When there's increased melanin in the skin from sun exposure,

the laser energy gets absorbed by epidermal melanin first —

before it ever reaches the follicle.

This raises the risk of post-inflammatory hyperpigmentation and burns,

while reducing the energy that actually reaches the hair root — making the procedure less effective.

That's why, during peak sun months (July–August),

if you've recently been to the beach or a pool,

it's safer to wait about 2 weeks before your next session.

That said, this doesn't mean summer procedures are off the table entirely.

If you've been mostly indoors and consistently applying sunscreen,

you can absolutely continue your sessions through the summer.

Session-by-Session Progress Timeline — What Does the Shedding Actually Look Like?

Based on what I see in my clinic,

here's how the experience typically unfolds session by session.

Session 1: Hair appears to shed around 2–3 weeks post-procedure,

then seems to grow back. This is when most patients start wondering, "Is this even working?"

Sessions 2–3: Regrowth slows noticeably,

and density visibly decreases. Most patients start feeling satisfied around this point.

Sessions 4–5: Coarser hairs are largely gone,

with only fine, sparse strands remaining.

Session 6 and beyond: Finishing up the inner line and deeper follicles.

This is the phase where dual-wavelength benefits are most pronounced.

But here's one thing that's really important to understand.

The reason results vary even with the same 6 sessions

comes down to the hair growth cycle.

Lasers only work on follicles in the active growth (anagen) phase,

and at any given time, only about 20–30% of hairs are in that phase.

That's why spacing sessions about 4 weeks apart

and treating different follicles at different stages of their cycle

is essential to avoiding missed hairs.

The 3 Questions My Patients Ask Most — Here Are My Honest Answers

Q1. If I complete all 6 sessions, will the hair never come back?

Honestly, that phrasing is closer to marketing copy than medical reality.

Laser hair removal achieves "permanent hair reduction" —

not "permanent hair removal."

After completing the full recommended course,

roughly 80–90% of hair typically stops growing back,

while the remaining 10–20% may become finer and lighter —

or regrow during hormonal shifts such as pregnancy or menopause.

That's why I recommend 1–2 maintenance sessions per year.

Once you know that, another question usually comes up.

Q2. Isn't a cheaper per-session price always the better deal?

This is one of the most common misconceptions I see, and it's easy to fall into the trap of looking only at the per-session cost.

If a package priced at ₩10,000 per session

uses only a single 755nm wavelength with a limited shot count,

you may end up with the inner line still present after 8 sessions —

and then need 4–5 additional sessions on top of that.

When you add it all up,

the total cost often matches or exceeds a 6-session dual-wavelength package.

Rather than focusing on the per-session price, I'd encourage you to ask

what device is being used

and whether shot counts are unlimited —

that's what actually reduces the chance of a disappointing outcome.

And this last point is one I always make sure to cover.

Q3. My skin feels hot and burning after the procedure — is that a side effect?

It's not a simple yes or no, because

you need to distinguish between a normal reaction and a warning sign.

A burning sensation for 2–3 hours immediately after the procedure,

mild follicular edema (slight swelling around the pores),

and light redness through the following day are all within the normal range.

However, if pain intensifies after 24 hours,

or if blisters, exudate, or scabs develop,

that could indicate a mild burn — and you should come in right away.

For the first 3 days after your session,

please avoid saunas, jjimjilbangs (Korean-style heated rooms), and intense exercise,

and be sure to apply a sunscreen of SPF 50 or higher.

That's the single most important step in preventing post-inflammatory hyperpigmentation.

If you take one thing away from today — for the underarms, wavelength combination determines results before session count does.


In my next post, I'll break down "the dark marks that remain even after laser hair removal" — the cases where it's not hair at all, but post-inflammatory hyperpigmentation. I'll walk you through real cases showing how to tell whether you need more hair removal sessions or pigmentation treatment on the same area. This has been Dr. Wi Young-jin.