The beauty spy

You won't see her, but she's there - in the salons, spas and shops - and she's happy to share her secrets on rejuvenating your hair. There's a bit of a trend for anti-ageing hair products at the moment and many of my friends think it's just another way for beauty companies to harness our paranoia about our looks and con us into emptying our wallets. Surely "hair ageing" can be dealt with quite painlessly by a good colourist. However, it seems that greyness is no more the only sign of hair ageing than wrinkles are the only sign of skin getting older.

Even if you are lucky enough not to go grey, your hair is still getting older. You'll notice in your forties that it's less abundant, but, according to Philip Kingsley - the world's most in-demand trichologist - hair's volume decreases gradually from the age of 25. It's common for hair to get drier as we get older and it loses "bounce" thanks to a decline in elasticity. The good news is that products and diet can make a dramatic difference. Most women don't eat enough protein to support their hair. I noticed a massive improvement in the condition of mine when I added some eggy breakfasts and a few helpings a week of fresh fish. I do think that some of our older beauty icons owe a lot to their hair: Catherine Deneuve, even Madonna. Good hair gives an overall impression of youth and good looks, even if the skin's been neglected - just look at the Duchess of Cornwall. The thick, shiny, creamy hair that replaced a greying mop of frizz when she married the Prince of Wales was, in truth, the key to her so-called "makeover".

For friends who suddenly notice, usually around the age of 40, that their hair needs some attention, I recommend the Kérastase range. Long trusted by professionals, it has something for every hair type. Their Reflection products, for example, are wonderful for protecting coloured hair, and I would struggle to survive without the Oleo Relax shampoos and conditioners, for dry or frizzy hair types.

Charles Worthington's excellent new Time Defy range contains sunflower extract to protect hair and mineral kelp to nourish, and the conditioners are especially good. Frédéric Fekkai, the Hollywood stylist, has a range called Ageless, if you want to splash out. His Creme Luxe Hair Treatment is pricey at £60 (www.hqhair.com), but who baulks at that for an anti-wrinkle cream these days?

Nikki Kinnaird, the founder of the Space NK beauty chain, on looking and feeling your best. Exercise every day is important, not just for burning calories, but for your state of mind, energy and stress levels. Getting fresh air is a great way to start your day. It's energising and a good way of getting your circulation going. Take care of your body all year round. In the summer, worrying about baring your body seems to become a priority, so keep up good habits all the time. I recommend using a body brush, exfoliators and firming creams. Antioxidants are always part of my day. Drinking green tea all day is an excellent way of making sure you take in plenty.