Types of acne scars: ice pick, boxcar, rolling

An acne scar is a change in the shape of the skin that stays after a breakout heals. A flat red, brown or white mark is a different thing: it changes only the color of the skin, and the American Academy of Dermatology (AAD) says those marks usually fade. This guide covers the scars. It explains each type, how to tell them apart in a mirror, and why the type decides which treatment a dermatologist picks. For every treatment option in one place, see acne scar treatment.

Two groups: sunken scars and raised scars

As a breakout heals, the skin makes collagen, the protein that gives skin its support. The AAD explains that the amount of collagen decides the scar:

• Too little collagen leaves a dent or pit. Doctors call these depressed or atrophic scars. This guide calls them sunken scars.
• Too much collagen leaves a firm bump. These are raised scars.

Sunken scars are far more common. The AAD says "most people who get acne scars develop depressed acne scars and often develop more than one type." A 2017 review in the journal Scars, Burns and Healing puts the share at 80 to 90 percent of people with acne scars. Raised scars are the smaller group, and the AAD says they are "more common in people who have darker skin tones."

The NHS describes the sunken kind as "shallow holes in your skin" and names two of them, ice-pick and boxcar scars. The three sunken types used on this page come from a 2001 paper in the Journal of the American Academy of Dermatology, which proposed a simple system of ice pick, rolling and boxcar scars. The authors said that once the type is known, a dermatologist can choose treatment to match.

Ice pick scars

An ice pick is a narrow, pointed tool, and these scars take their name from the small, deep hole it would leave.

• What they look like. The AAD calls this "the most common type of acne scar" and says "it looks small but goes deep into the skin." The NHS says this type of scar "looks like a deep pore."
• Size. The 2017 review describes them as narrow, V-shaped tracts under 2 millimeters wide that reach the deep layer of the skin, or even the fat below it.
• How common. The same review says estimates put ice pick scars at 60 to 70 percent of sunken acne scars, boxcar scars at 20 to 30 percent and rolling scars at 15 to 25 percent. It adds that the exact numbers are hard to calculate.

Depth makes these scars hard to treat. The 2017 review says their depth makes them resistant to treatments that work on the surface. A 2018 review of lasers and other energy devices, by the same authors, found ice pick scars responded least to fractional CO2 laser, because they are likely deeper than a laser can reach. Dermatologists often use focused treatments instead, such as a strong acid placed into each scar, described in chemical peels for acne scars.

Boxcar scars

A boxcar is a railway freight car with straight sides, and these scars have the same shape: steep walls and a flat floor.

• What they look like. The AAD says they "cause a round or oval-shaped depression in the skin" and are "wider than ice pick scars but not as wide as rolling scars."
• Size. The 2017 review gives a width of 1 to 4 millimeters, with sharp edges.
• Depth matters. The review says shallow boxcar scars respond better to resurfacing treatments, which remove or heat the top layers of skin. Deep boxcar scars respond less well to those surface treatments.

Rolling scars

Rolling scars are the widest sunken type. The AAD says "this type of scar is wide and shallow. When someone has many rolling scars, the skin can have a rolling or wavy appearance."

The 2017 review explains why they form: bands of scar tissue connect the skin to the layer below and pull it down. The scars are usually 4 millimeters wide or more, with soft, uneven edges. Because the pull comes from under the skin, the review says rolling scars need treatment below the surface. That is the job of subcision, a procedure in which a dermatologist slides a needle under the scar to cut those bands. See subcision for acne scars.

Raised scars: hypertrophic, keloid and papular

The AAD lists three raised types:

Type	What the AAD says
Hypertrophic scar	Feels firm. Usually on the jawline, chest or back. Often appears 1 to 2 months after a breakout clears
Keloid	Grows larger than the breakout that caused it. The first sign is thickening skin, usually 3 to 12 months after acne clears
Papular scar	Skin colored or lighter than the person's skin tone. Usually on the nose, chin, jawline or back, and "can be mistaken for acne"

The NHS describes the first two. A hypertrophic scar is "usually raised and firm" and "usually fades and flattens over time." A keloid "grows to be bigger than the original wound" and "does not usually flatten or fade without treatment." The AAD adds that raised scars are more likely to itch or hurt than sunken ones. The guide raised acne scars covers treatment, and back acne scars covers the chest and back, where raised scars often form.

Flat marks that change only the color

After a pimple heals, many people see a flat spot and call it a scar. The AAD uses a different name for it. A flat spot that is red, pink, brown or bluish gray is post-inflammatory hyperpigmentation, or PIH. It says PIH "usually fades over time," and that "treatment can clear the spots more quickly." Flat white spots, which doctors call hypopigmentation, are in the same group.

A new scar can have both problems at once. The AAD's overview says a new scar may show a dent or bump "along with some discoloration," and that "over time, the discoloration usually goes away. However, the scar remains." So a red dent may lose its redness and still stay a dent. For the flat marks, see dark marks after pimples and how long dark marks take to fade.

How to check which type you have

Stand at a mirror in daylight, with light coming from one side. Side light makes dents and bumps cast small shadows.

What you see and feel	Likely type
A narrow, deep hole, like a large pore	Ice pick
A round or oval dent with steep edges and a flat floor	Boxcar
A wide, shallow dip; many of them make the skin look wavy	Rolling
A firm bump that stays inside the old breakout area	Hypertrophic
A bump that keeps growing past the old breakout area	Keloid
A small, soft, skin-colored bump on the nose, chin, jaw or back	Papular
A flat spot with a smooth surface, only the color has changed	Mark (PIH), usually fades

Most people have more than one type. The 2017 review says the types can be hard to tell apart and often appear together in the same person. That is why a dermatologist's exam comes before any treatment. The AAD says the dermatologist will pay close attention to "the types of acne scars on your skin and where they appear," because "ice pick scars require different treatment than rolling scars."

Why the type decides the treatment

The AAD's scar pages and the two reviews link each type to different treatments. The table sums up what those sources say. Use it to prepare for a talk with a dermatologist, who makes the final choice.

Scar type	Treatments the sources link to it
Ice pick	A strong acid placed into each scar; ice pick scars respond least to lasers
Boxcar	Resurfacing lasers and peels, which work best on shallow boxcar scars
Rolling	Subcision, fillers and lasers
Hypertrophic	Steroid injections, laser, prescription medicine, silicone gel
Keloid	Several treatments together; some keloids return
Papular	Lasers

Each option has its own guide: laser treatment, microneedling, dermal fillers and subcision. Creams have a smaller role. The AAD says a retinoid or salicylic acid "can make scarring less noticeable" only when scarring is mild. See tretinoin for acne scars.

What makes scars more likely

The AAD names three risks: deep acne such as cysts and nodules, picking or squeezing breakouts, and a close blood relative with acne scars. It also says "some people develop acne scars when blackheads or whiteheads clear," so shallow acne can scar too. The best protection is treating acne early. The AAD says treating mild acne early means "deeper acne breakouts, which are more likely to cause scarring, never develop." The guide should you pop a pimple explains why squeezing raises the risk.

When to see a dermatologist

See a dermatologist when acne starts leaving dents or bumps, when a bump keeps growing, or when you want to treat scars you already have. Bring a list of every acne treatment you have used in the past two years, which the AAD asks for before scar treatment. Skinli is not a doctor and cannot tell a scar type from a photo. It can help with the acne that causes new scars: the free Skinli acne plan builds a routine around benzoyl peroxide 2.5 percent and adapalene 0.1 percent and tells you when your skin needs a doctor. Whether a scar will fade on its own is covered in are acne scars permanent.