In your thirties it's all about glamming up, but at forty less not more is the secret to turning back the beauty clock says Hannah Betts

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It is a truth universally acknowledged that, come 30, a woman is obliged to smarten up her act. Pre the big 3-0, mere toothbrushing may be considered sufficient by way of glamour. Hair may be left unbrushed, hands artlessly unmanicured, pant topiary fauvist. Insouciance is all, with the one proviso: wear sunscreen.

However, as the third decade dawns, matters require a rigorous taking in hand. One’s hairdresser becomes one’s ally, one’s demeanour necessarily sleeker, and a sheen of tinted moisturiser/BB cream may be acquired. For what says “alluringly nonchalant” at 19, says “grubbily unwashed” at 34.

You know all this, of course, dear readers, being nothing if not glossy. Yet a new grooming equation must be learnt at 40, and it is nothing about perfectionism, everything about letting a few things slide.

I first stumbled upon this revelation at the hands of my hairdresser/the man I love, Andreas Wild, shining star of Aldford Street’s John Frieda ( ). As ever, I was opining about my pathological hatred of helmety, blow-dried hair. “It makes me look like an anchor woman,” I bleated. “Well, yeah,” the great man deadpanned Teutonically, “we don’t make you too done, or with everything else it will be Just Too Much”. (By “everything else” he refers to my penchant for a full maquillage plus vaguely theatrical clothing.)

At this point, birds flew backwards and lightning rent the skies. For, what pulls you together at 30, can add a good ten to 20 years at 40. Since this Damascene moment, I have established various anti-ageing axioms of my own. Viz:

Foundation must become ever more subtle/ translucent/ natural-looking (a cinch as, industry-wide, it is tending to)

Less is not only often more, but heaviness in one area must, must, must be balanced with low-keyness in others, unless one’s look is ageing drag queen (which, admittedly, mine often is)

Never do hair, face and nails (compare haute fashion bitch Carine Roitfeld with her smokey eyes, vampy talons, yet rock chick bird’s nest)

Shortish claws only, please

Beware deadeningly flat neutrals. Nothing is more suggestive of a “Country Casuals” face. Luminosity is your friend, colour by no means out of bounds

Keep eyebrows as full-yet-shaped as possible, powder them rather than pencil, a shade darker than your sprouting if blonde, a shade lighter if brunette (although I do allow myself the occasional lurch darker by night if I’m feeling a tad Twilight)

Always work in some element of modernity – this season’s slightly tricky, but ultimately thrilling grey Chanel lowlighter, Ombre Contraste in Notorious (020 7493 3836); a youthfully beachy, or bed-heady blow (Master Wild excels at them); or yellow nails (that’s varnished, not mouldering).

I’m not going to suggest that old chestnut “wear something colourful close to the face”, but I am totally thinking it. See you anon, slap fans.