While most cosmetic companies spend thousands on glitzy publicity campaigns, Liz Earle Naturally Active Skincare is famous for not advertising. It's when you meet founder Liz Earle in the flesh, that you realise she's her own best advertisement.

At 45, Liz has the luminous skin of someone 20 years her junior. But despite being elegantly groomed and perfectly coiffed, hers is a very real, approachable beauty. There's no trace of the surgeon's knife or needle and she's happy to pull faces to illustrate her own (practically invisible) wrinkles.

This savvy businesswoman, who received an MBE for services to the beauty industry in 2007 and presides over a multi-million pound company, knows the value of her own brand.

"I think that if you have a great product, you don't need to advertise it," she says simply.

"I take the long term view - if our customers like something, they'll tell others. That's the way we've built a strong business."

Such sensible common sense is rare in an industry built on hope and conjecture, but it's obviously worked - a bottle of her Cleanse And Polish Hot Cloth Cleanser sells every eight seconds and fans gush about the rest of the botanically-inspired range in online forums and on YouTube.

Liz, a beauty journalist before starting her company with friend Kim Buckland in 1995, has now distilled the secrets of her success in a new book, Liz Earle's Skin Secrets.

It's almost more coffee table book than how-to guide, illustrated with photos of Liz, her friends and family, looking fabulous. But refreshingly, it's also filled with sound advice on looking - and feeling - good, at any age.

Liz says she wrote the book in response to "overwhelming customer pressure."

"I've been in the beauty business for over 20 years. I get asked time and time again the same questions, ranging from 'what's a moisturiser' to 'tell me the properties of propylene glycol'," she explains.

"I've tried to answer all the questions I've been asked.

"I've done a shedload of research. I've learned so much more about what goes on behind the scenes - about how skin care is put together, what are the ingredients that really work and how to use products to their best advantage.

"I'm not preaching, I just want people to be informed."

Somewhat surprisingly, the book doesn't plug Liz Earle Skincare.

"I made a conscious decision not to do that - I wrote it as an independent observer," she says.

"I've had my own skin problems - I've had a long struggle with eczema, but I think now I've finally cracked it and I've got a coping strategy that will help others.

"Obviously I use my own (products). Even if you don't use my range, I want to give you information about what to look for in others.

"Good skincare is about good ingredients - it's like cooking. Good ingredients will result in a delicious dish - but if you don't have good ingredients then you'll never make it tasty, no matter what you do."

She's annoyed that while alcoholic drinks are not required to carry stringent labelling, "I have to label what's in my products down to the last molecule."

The book is a real family affair - Liz's mother and her daughters both feature in photographs, which were taken by her husband, photographer Patrick Drummond. She jokes that her two sons are annoyed they don't appear.

The photographs in the book make Liz's life look idyllic, but she confesses she's sleep-deprived thanks to her family commitments, the demands of the skincare company and the day-to-day hassles of life on the couple's organic farm in Wiltshire.

"We've just started lambing," she grimaces.

"It's hard work but we wanted to be active farmers, not just have a big house and a garden. It's not a relaxing hobby!"

She travels a great deal, both within the UK - the skincare company is based on the Isle of Wight - and abroad.

When we meet she's only recently returned from a work trip to Malawi and Uganda, where she's been working with a women's co-op that produces the shea butter used in her products. She also sources raw materials from similar groups in Morocco and Kenya, where she has a house.

"I can relate better to these women now I'm a farmer," Liz says.

"It's very humbling - if you don't buy from them they can't keep the school running and keep their families going."

Liz Earle Naturally Active Skincare is now available in 82 different countries, including the US, thanks to a chance endorsement from the beauty gurus at American Vogue.

Liz says she's constantly dreaming up new additions to the range, with hair care products the next on her to-do list.

The one thing she's not interested in pushing is any kind of 'anti-ageing' potions.

"I'm not anti growing old. Ageing is not a disease to be cured," she says.

"I don't want to look old before my time, but we've lost sight of the balance - getting older needs to be seen in a positive way."

Liz says her products focus on getting the skin in its best possible condition - whatever the age of its owner.

"For me there are more important things to worry about than the state of my skin. Wrinkles shouldn't be one of them. We've got to put things in better balance, be more focussed on what's important in life," she says, sounding exasperated.

"I don't want to be part of that pressure. I deliberately had myself photographed with wrinkles in the book. There's no retouching," she laughs.

"I've got lots of small lines."

Liz Earle's Skin Secrets - How To Have Healthy Beautiful Skin Naturally by Liz Earle is published by Kyle Cathie, priced £19.99. Available now.