Jun 06, 2026

What Causes Acne? A Dermatologist’s Guide to Why Breakouts Happen

Acne affects over 80% of people at some stage. Consultant Dermatologist, Professor Nicola Ralph of the Institute of Dermatologists explains what causes acne, the role of hormones and genetics, and when to seek help.

Acne affects more than 80% of people at some point in their lives, across every age and skin type. Despite how common it is, what actually drives a breakout is still widely misunderstood. For Acne Awareness Month, Consultant Dermatologist and co-founder of the Institute of Dermatologists, Professor Nicola Ralph, explains the real causes of acne and what they mean for managing your skin.

The short answer: acne happens when pores become clogged with oil, dead skin cells and bacteria, which triggers inflammation. Hormones and genetics are the biggest underlying drivers. It is not caused by poor hygiene, and for many people it is not something they simply grow out of.

What is acne, exactly?

Acne occurs when the pores become blocked with oil (sebum), dead skin cells and bacteria. This, combined with the presence of bacteria on the skin's surface, sets off an inflammatory response — producing the range of lesions associated with acne: blackheads, whiteheads, papules (red bumps), pustules (pus-filled lesions), and the deeper cysts and nodules seen in moderate to severe cases. Left untreated, acne can also lead to scarring.

It most commonly appears on the face, followed by the back and chest, and can affect people anywhere from infancy to their 60s, 70s and beyond.

Close-up of acne on the cheek showing papules and post-inflammatory marks — *Acne on the cheek — papules and post-inflammatory hyperpigmentation. Image: DermNet*

Acne on the forehead showing comedones and papules — *Forehead acne — comedones and early papules. Image: DermNet*

Acne on the cheek and jaw showing inflammatory papules — *Inflammatory acne along the cheek and jaw. Image: DermNet*

Acne across the full face showing widespread papules and hyperpigmentation — *Widespread facial acne with papules and hyperpigmentation. Image: DermNet*

What actually causes acne?

Several factors work together rather than a single cause:

Overactive oil glands. Sebaceous glands produce excess sebum, which feeds the skin's natural bacteria, enabling them to thrive.
Bacteria. A normal skin resident called Cutibacterium acnes uses that oil as an energy source and multiplies, contributing to the inflamed spots characteristic of acne.
Dead skin cells. These mix with oil and clog the pore.
Hormones. Androgens, present in both men and women, increase oil production. This is why acne is so common during puberty, menstruation and pregnancy, and why hormonal shifts can drive adult acne for years.
Genetics. A family history of acne is common and plays a significant role.

Does diet cause acne?

Diet alone does not cause acne. That said, some evidence suggests high-glycaemic foods and excessive dairy may worsen breakouts for certain people. Keeping a simple food diary can help you identify personal triggers — but a healthy diet supports clear skin rather than curing acne on its own.

Does stress make acne worse?

Stress can exacerbate acne. It raises cortisol levels, which affects other downstream hormones and can intensify breakouts. Managing stress through exercise, rest or relaxation techniques can have a positive knock-on effect on the skin.

Will I grow out of acne?

Not necessarily. This is one of the most common myths Professor Ralph hears in clinic.

"Approximately 85 to 90% of teenagers experience some form of acne, and while most do not scar, scarring is the signal that it is time to move beyond over-the-counter products and seek medical advice. Acne can also develop later in life, even in people who never struggled as teenagers. It is common in the twenties, thirties, forties and beyond, and for women in particular, hormones can play a major role for much of adult life."

— Professor Nicola Ralph, Consultant Dermatologist, Institute of Dermatologists

So while many teenagers improve with age, there is no guarantee anyone will outgrow it. The more important signal is scarring or persistence. If acne is not responding to over-the-counter products, that is the point to seek advice rather than waiting it out.

Professor Nicola Ralph, Consultant Dermatologist at the Institute of Dermatologists — *Professor Nicola Ralph, Consultant Dermatologist and co-founder of the Institute of Dermatologists*

When should I speak to a professional?

It is worth getting in touch if:

Your acne is affecting your confidence or quality of life
The products you have tried are not working
Your acne is leaving scars

There are many effective treatments available with a high success rate, and the right approach depends on your skin. A good home skincare routine also plays an important part in preventing flares — which we cover next in this series.

Frequently asked questions

Is acne caused by poor hygiene?

No. Over-washing or scrubbing can actually irritate the skin and make acne worse by stimulating oil production. Gentle cleansing is the goal.

Can adults get acne?

Yes. Adult acne is common, particularly in women, and is often linked to hormones rather than anything you are doing wrong.

Does acne always scar?

No. Most people do not scar, but scarring is a sign that acne should be assessed and treated rather than left.

Will acne go away on its own?

Sometimes, but not reliably. If it is persistent or scarring, professional treatment is the better route.

Acne Awareness Month at the Institute of Dermatologists

If acne is affecting your skin or your confidence, our team is here to help. Contact the Institute of Dermatologists on 01 912 3030 or info@instituteofdermatologists.ie to talk through your options.