Unless you were extremely lucky, chances are, when you were a teenager you experienced acne of some sort, whether it was a smattering of spots or a serious outbreak.
By the time you reached adulthood, though, with a bit more luck the zits disappeared.
But what if they return? Why do some people suffer with acne way beyond adolescence?
"There are many reasons as to why adults can experience acne," says Lisa De-la-Plain, professional beauty therapist and co-founder of Beauty Flash.
"One, in particular, can be a change in hormonal activity. As we move through the various stages of our life, our hormone levels fluctuate, and an imbalance can lead to breakouts.
"This is because producing more hormones stimulates the oil glands and hair follicles in the skin, leading to an inflammatory reaction and acne." Then there are environmental factors, such as pollution and weather, that can cause a flare-up.
"An increase in oil production, due to heat and humidity in the summer and surface dehydration in the winter months, can all encourage an acne breakout," De-la-Plain says.
If your experience of acne as an adult is different to your teenage years, that's because your skin has changed, too.
"Your skin cell turnover starts to slow down as early as your 20s. This means dead skin cells accumulate on the surface of the skin, which can clog your pores and cause acne," De-la-Plain explains.
Plus, you're more likely to get spots around your mouth and jaw, as opposed to the T-zone.
"This is a tell-tale sign for hormonal flare ups, as oil glands, stimulated by excess hormones, are found in the chin area."
So, what can be done to tackle the problem? Skincare is the first step, but it's not just a case of whacking on some tea tree oil and hoping for the best.
A more holistic approach is best, our expert advises. Here's what to do if you're suffering with adult acne…
Go back to basics "A simple routine is often the most effective for acne sufferers, and cleansing and treating your skin twice a day is the best way to keep breakouts at bay," De-la-Plain says, but you should tailor your products according to your skin type.
"If your skin is prone to oiliness, choose a cleanser like Medik8 Clarifying Foam, which uses salicylic acid to stimulate natural exfoliation to help clear clogged follicles.
Medik8 Clarifying Foam, €24, Skin Shop
The Inkey List Salicylic Acid Cleanser, €12.95, Look Fantastic
"If you have sensitive skin, look for products containing lactic acid or hydrating ingredients like glycerine, as these aren't as drying as those made for oilier skin types."
Be careful if you have started investing in anti-ageing skincare too, she warns: "These creams can be very rich, overload the skin and cause breakouts in acne-prone individuals.
"Look for oil-free products like Dermalogica Oil Free Matte SPF 30, which will protect you from the ageing effects of UV and unwanted spots."
Dermalogica Oil Free Matte SPF 30, €54.45
Eucerin Dermo Purifyer Adjunctive Soothing Cream,€8.99, Boots
Kate Somerville Oil Free Moisturizer, €62.09, Space NK
Lose the layers
While it may be tempting to load up your skin with every anti-acne potion and lotion you can find, that could irritate your spots and make them worse.
"If you still want to use several products in your routine, to target other skin issues like sun damage and wrinkles, make sure you layer them from thinnest to thickest," De-la-Plain says.
"If you don't do this, they may cancel each other out. For example, acne ingredients like benzoyl peroxide, salicylic acid and lactic acid shouldn't be mixed with retinol, as it will break down your skin barrier and lead to irritation."
Pick the right spot treatment
With so many spot treatments on the market, how do you know which is best for your you?
"Consider what type of acne you have," De-la-Plain says. "Do you have inflamed red bumps? If so, you'll need a spot treatment containing benzoyl peroxide, which kills bacteria and calms redness.
"If you have blackheads and whiteheads, you'll want something with salicylic acid like Dermalogica Medibac Overnight Clearing Gel. It reduces excess oil and exfoliates dead cells from the skin's surface."
Dermalogica Medibac Overnight Clearing Gel, €47.20
Don't skip moisturiser
"While it might seem like a good idea to skip the moisturiser, if skin becomes too dry, the oil glands tend to overproduce oil and can make acne worse," De-la-Plain says. "Hydrating the skin properly re-balances oil glands and helps control breakouts.
"Pick a light or gel consistency, like Medik8 Balance Moisturiser, with glycolic acid activator. It has anti-inflammatory properties, which also controls shine and oil production."
Medik8 Balance Moisturiser, €42.90
Be a sleeping beauty
We all know that getting enough 'beauty sleep' helps our complexion, but did you know that your bed could be causing breakouts?
"Not washing your pillowcase regularly can result in a build-up of dirt, dead skin cells, and even breakout-causing bacteria," De-la-Plain warns.
"To prevent new breakouts from developing overnight, switch your pillowcase either every few days or daily, dependent on how prone to acne you are.
"Even the type of pillowcase matters. Although silk pillowcases are recommended for fighting fine lines and frizz, breathable fabrics like cotton may be better when it comes to preventing breakouts."
If all else fails, see a professional
Everyone suffers the odd zit, but if your adult acne is persistent, don't suffer in silence.
"If you've tried everything, you're still breaking out and your acne is causing psychological problems or is impacting your work or social life, it's time to visit your GP," De-la-Plain says.
"If your skin issues are severe, they will refer you to a dermatologist for a further skin assessment, to try and solve your concerns."