In this regular series, Ageless Beauty, The Telegraph's beauty experts Annabel Jones and Lisa Armstrong tackle the conundrums they've been searching for answers to, and share their favourite tips and tricks. This week, they discuss how often you should wash your hair. Ask them your questions below...

Amidst the thousands of emails we receive on the fashion and beauty desk every week, it was one about retinol from Dr Michael Prager that caught my eye. "Retinol has been touted as a holy grail of skincare, but I've never been a fan," wrote Prager. "True, using retinol can result in a modest increase in skin collagen by a factor of 1.3. However, the side effects far outweigh the benefits: red, sore, flaky skin and extreme light sensitivity." After using it and going on a Caribbean holiday, Prager returned with dark blotches on his forehead. "That was the end of my relationship with retinol," he says. "While it disperses pigment clusters, it also strips the protective dead cell layer, making your skin vulnerable to damage. This waxen, overly sensitive look is far from what I consider desirable or practical."

That really got me thinking, because someone else I hugely respect in the beauty industry has been saying something similar for years. Alexandra Soveral, the facialist-cum-bio-chemist-cum-mother-of-organic-skincare, sits some way along the beauty continuum from Prager, who rose to prominence as a dispenser of injectables to the A-list. Soveral takes a more holistic approach, believing in the power of massage (hand not mechanical) to give skin a lift, tone and glow. In her 50s, she - and her regular clients - are proof this approach works. If both she and Prager, with more than half a century in skincare between them, are raising questions about retinol, it's time to listen.

As a reminder, retinol - and retinal, a stronger formulation - are forms of vitamin A. In moderation, they're a great tool. "Vitamin A is a powerhouse for skin health, playing a crucial role in cell division, tissue repair, and maintaining the skin's protective barrier," says Soveral. "Used in the right amounts, it helps keep skin smooth, firm and resilient by encouraging healthy cell turnover and guarding against environmental damage. "But," she continues, "the skincare industry, alongside dermatologists, have disregarded the safety guidelines and encouraged consumers to overuse retinol." (That's just changed in the EU, where new legislation has been passed that restricts the use of all forms of vitamin A in skincare products.)

The results of overzealous retinol application are all around us, particularly in mid-life and older women: skin looks like parchment. "Too much retinol accelerates skill cell division in an unhealthy way," says Soveral, "leading to issues such as inflammation, acne, rosacea, hypersensitivity and hyperpigmentation. It actually speeds up ageing."

For optimal results, Soveral recommends vitamin A in its most bio-available form, ie (ideally organic) broccoli, sweet potatoes, carrots, leafy greens, fish... and using cold-pressed oils containing vitamin A. Rosehips are a rich source - and there are some reasonably priced options. The Rolls Royce is Soveral's Alpha Water Serum and Delta Lipids Oil. If I could only have two skin care products in my bathroom, it would be these.

Designed to be used in tandem, they're highly active but gentle and long-lasting with trace amounts of natural vitamin A. "Instead of forcing cell division, it will just give them a gentle boost to not become sluggish," says Soveral. "In the end, nature knows best."

My first encounter with retinol was in no uncertain terms a car crash. I was in my early 30s and keen to reap the glow-inducing benefits I'd heard (and seen) so much about, but I aborted the mission before the month was up due to an intolerable case of the "retinol uglies".

The uglies is TikTok lexicon for the settling-in phase of flaky, inflamed skin. Mine was so angry looking, a friend gasped before asking, half jokingly, if I'd contracted an infectious skin disease.

I'm told by retinol evangelists that if you stick it out, your complexion repays you with an otherworldly glow. Sadly, I'll never know; I pulled rank for the sake of vanity and steered clear of retinol for the next decade - at least.

To be fair this was 20 years ago when retinol formulations were far less sophisticated than they are now. These days retinoids are often delivered in skin-friendly liposomal capsules to minimise irritation and transport the molecule directly where it needs to go. Plus, there are varying retinoids to choose from like the ever-popular retin-A (retinaldehyde) which is deemed a gentler alternative to pure retinol.

There isn't a dermatologist I know who doesn't believe in tretinoin, the prescription retinoid that's scientifically proven to have a role in acne and wrinkle reduction. Furthermore, long-term studies have shown that retinoids improve collagen production over time - more collagen, and firmer skin. All in all, the evidence is hard to dispute.

That said, I'm often asked to abate the concerns many people have about whether or not to use retinol. So I recently asked the dermatologist Dr Ellie Rashid about whether retinoids do indeed thin the skin. Her response was balanced. It does compromise the top surface of the skin temporarily, hence why SPF and minimal sun exposure is recommended.

But, she argued, cell turnover slows considerably with age, thus speeding it up isn't necessarily a bad thing. One could argue it's merely restoring the status quo. If you use the right dose and formulation (she's a fan of CeraVe) for you, the benefits of retinol generally outweigh the cons. Especially if you suffer from hyperpigmentation, fine lines or dullness.

I have been using a retinoid cream on my hands and décolletage for the past six months or so, as they have seen more UV rays than I care to admit. Does that make me a fan? As irritating (pardon the pun) as it sounds, I'm still on the fence.

I believe retinol has its place. I trust the experts who advocate for it and there's no doubt it works at fading hyperpigmentation and evening out skin tone, so long as you don't overuse it and apply SPF50.

But I also think, like with all anti-ageing protocols, that in the end it is a personal choice. If your wrinkles and pigmentation bother you enough to deal with some minor irritation then it's a useful tool alongside a good barrier cream and religious UV protection - especially in winter when the sun is hiding out.

I dip in and out, and when I do I use gentle formulations that are slower to work. When it comes to my hands I'm unapologetic. They get a liberal coating every other day - and it's made a visible difference to pigmentation and fine lines.

If, however, I could give my teenage self a talking to, the girl who slathered on a coconut-scented SPF8 sun oil with abandon, my advice would be simple: stay out of the sun, apply a good full spectrum SPF daily, mitigate stress, eat well and you won't be debating the pros and cons of anti-ageing protocols decades later.