Hello, podcast fan.

Consider this your invite to the UK's biggest podcasting party.

We're heading to Sheffield from the 4th to the 6th of July

for the BBC Sounds Fringe at the Crossed Wires Festival.

We'll be joined by some of the biggest names in podcasting,

including Sarah Cox, Charlie Hedges, Russell Kane,

and some bloke called Greg James doing his Radio 4 show called Rewinder.

You can watch live shows of your favourite podcasts, and the best part is free.

To book your free tickets, go to crossedwires.org slash fringe.

BBC Sounds, music, Radio, podcasts.

Welcome to The Best Things Since Sliced Bread, a podcast from BBC Radio 4 that's all about separating science fact from science fiction.

I'm Greg Foote and I just want to find out if the latest wonder products and social media crazes really are all they're cracked up to be.

Today, we're investigating caffeine hair products,

shampoos and tonics that promise to help you battle thinning hair. Are they the best instant sliced bread or marketing BS? Loads of requests for these on Twitter, including from Catherine

Smith, Michael Taylor, Ingrid, Susanka and others. If you've got something that you'd like us to dig up the evidence for, or if you'd like to join the conversation on Twitter, I'm at Greg Foote or use hashtag BBC sliced bread. I've got two guests to help me run caffeine shampoos and tonics through the evidence mill today. The first is Ian Carmichael, senior director in Styling at Trevor Sorby, the hair salon,

and a man who styles many high-profile heads, including Her Majesty the Queen.

Thanks for joining me, Ian.

You're welcome.

So Her Majesty the Queen, what an amazing person to cut and style.

Is there anything you can tell us about her hair?

She has lovely hair. That's all I can tell you. She has wonderful hair.

Does she use caffeine shampoo?

...