Are your tresses looking tired? Has your hair gone ho-hum? Forget the flat, single-tone dye job of years gone by - the hottest hair fashion these days is highlighting and lowlighting. These aren't mousy shades, mind you; today's tones are decidedly pronounced and eye-catching. We asked Millie Jones, senior colourist at London's Jo Hansford Salon, for the low-down on the technique.

What's the difference between a highlight and a lowlight?

Quite simply, a highlight lightens and brightens the hair, while a lowlight darkens and deepens it. Think blonde, gold and chamomile tones for highlights; reds, plums and aubergine shades for lowlights. Usually, two or three colours are used throughout the hair for a multifaceted, shimmering effect - any more than that and the hues can lose their contrast and look a bit muddy.

Why have these processes become so popular?

Highlights and lowlights provide a great way to update your look without making too dramatic a change. They're ideal when you're growing out a style and you're in that awkward, in-between stage when you don't really like your hair.

Highlights and lowlights also allow you to brighten your hair, especially during winter, when we could all use a little pick-me-up. At this time of year, many women's hair is naturally lighter on the ends after spending time in the sun during the summer. As a result, hair often takes on a dull, drab appearance. Highlights and lowlights can really brighten up your look.

Which hair types are best for highlights and lowlights?

Actually, any length, style or condition of hair can benefit from highlighting or lowlighting. Whatever your natural colour, you shouldn't go more than three or four shades lighter or darker, as the results will be too harsh and unnatural.

Will highlighting or lowlighting damage my hair?

No. These days, colourists often use semi-permanent vegetable dyes so there's no damage to hair. Even when permanent colours are used, the process plumps up the hair cuticle so it instantly looks thicker and fuller. In any event, you should always add a conditioner to help maintain the colour and texture.

How much can I expect to pay?

The cost depends upon a number of factors, such as how many highlights or lowlights you have (you can either get a 'full head' or a 'half head'), the length of your hair, and the experience of the colourist. Since he or she will apply multiple shades, it's fairly labour- intensive. For a full head, expect to pay between £115 and £145.

How often will I need to have a top-up?

It will depend a lot on the length and style of your hair and the effect you're trying to achieve. Obviously, a short, cropped style will show regrowth much faster so you'll need a top-up every six to 12 weeks. A longer, less layered style need only be touched up four times a year.