There can’t be a teenager in the land who hasn’t glared into the mirror one evening and groaned. “Why tonight? Why a mega red and yellow spot on my hottest date ever? It’s like there’s a cosmic plot against me.” Well, according to a radical new theory, that may be exactly what is happening. That jeering pustule may be a big red stop light specifically designed to say: “You are not ready for nookie.”

This controversial idea about why we suffer from acne is just part of a rethink of this condition in the laboratory of Dr Terence Kealey, a skin specialist at the University of Buckingham. “We’ve developed a test-tube model of acne and found that the standard explanation for why teenagers get spots is largely wrong,” he says. Within a few years these findings could be leading to sophisticated new treatments.

The big new finding of Dr Kealey and his team is that acne is caused by the immune system. Even more important is the discovery that there are two different types of acne which are the work of two of the many chemicals involved in maintaining our immune defences. “The standard information leaflets tell you that whiteheads and blackheads can progress to an inflamed spot by a mysterious process that is never clearly explained,” he says. “What our system shows is that the relatively mild whiteheads and blackheads are produced by one of these chemicals, while the inflamed pustules are produced by the other.”

What causes these immune chemicals to become active in the first place? That’s the responsibility of bacterium — Propionibacterium acnes — which feeds on the sebum, an oily secretion in the hair follicles. Proteins on its coat are detected by the immune system, which then mount a defensive response.

Dr Kealey found out what was going on by using skin cells taken from women who were having plastic surgery. “Animals don’t get acne so we had to use human skin cells. Face-lifts provided a good supply that allowed us to grow skin in a test tube,” he says. Left alone, the cells produced normal smooth skin. The big discovery was that to produce full-blown acne you just add one of the two immune-system chemicals.

“If we added one called IL-1A you got perfect whiteheads or blackheads,” he says. “If you added another one, TGFA, you got the inflamed pustules. Each works in different ways. One causes the wall of the hair follicle to shed cells much faster, while the other makes the follicle grow oddly so it bursts.” Already there are drugs that can block IL-1A or TGFA, which might be suitable to treat acne.

But this still doesn’t explain why our immune system should want to pull this horrible trick on us in our teenage years and how it could possibly have an evolutionary advantage. “Everyone is so familiar with adolescent acne that they don’t realise just how mysterious it is,” Dr Kealey says. “It affects about 85 per cent of people between 14 and 18. This suggests that it’s normal. I think it’s very likely that we are meant to develop it.”

Even odder is that it’s one of those physical features that mark us out as human beings, like standing upright, or having a big brain. No other primates get it. When we turned into naked apes several million years ago and lost the hair off our bodies, acne was an unwelcome side-effect.

“It’s still a theory,” Dr Kealey says. “But another distinctive human trait is that we have a much longer period of childhood than any other animal because we have to learn a whole range of social and language skills to fit into the group. Having babies before you’ve got those under your belt could make it less likely your children would survive.” So spots are a cunning way of putting off potential lovers and, therefore, avoiding having children at too young an age. This is because we are hard-wired to fancy only healthy people and spots give people the appearance of illness despite there being none.

If the Government really wants to cut teenage pregnancies, perhaps it should abandon contraceptive-advice programmes and ban all acne treatments instead.

"IT CAN RUIN YOUR LIFE"

“I thought I had escaped the worst effects of acne until I was just 17,” says Susan, “but then it really hit me. Suddenly I was covered with bumps and spots. The first thing that goes is your self-confidence and you can get really depressed. I didn’t get into taking antidepressants, but I know a lot of people with bad acne do and I’m not surprised — anything not to feel so yucky.

“Your social life takes a dive. Even if someone does want to go out with you, you feel so self-conscious that often it’s easier to say no. If I did go out, I’d have to spend hours putting on the full make-up and when we got somewhere it was straight into the toilet to check how I looked. By that time I was so sorry for myself I was in a real mood. I would only talk with my hand in front of my face. Not many boys asked twice.

“It wasn’t even as though I could really get into studying. Even in class I spent most of my time wondering how the spots were looking. I’ve learnt since that about 20 per cent of people who get them badly take time off school. If you say the word ‘spots’ it sounds really small and unimportant, but they can ruin your life. For a while anyway.”

BANISH THE BLEMISH

Complementary therapies include the B vitamin niacinamide, anti-bacterial tea tree oil and 90mg zinc daily for three months.