When we think about hair growth, most people jump straight to nutrition, hormones, or topical treatments. But there is a really interesting and still emerging area of research looking at how light, specifically blue light, interacts with proteins in the hair follicle to influence growth.

This actually came up in tonight’s skin science lecture, and it is one of those topics that really sticks with you because it links together so many areas we do not always think about, including light exposure, cellular biology, and hair growth.

At the centre of this is cryptochrome 1 (CRY1), a blue light sensitive protein traditionally known for its role in circadian rhythms. Recent dermatology research now shows that CRY1 is not only present in human hair follicles, but may actively regulate the hair growth cycle.

What Are Cryptochromes?

Cryptochromes are proteins that respond to blue light and help regulate the body’s internal clock. They have been studied for years in relation to sleep, metabolism, and cellular timing.

What is newer, and particularly relevant for us in aesthetics, skin, and hair science, is that these same proteins are active in the skin and hair follicles, where they appear to influence cell behaviour, growth, and regeneration.

CRY1 in the Hair Follicle

CRY1 is strongly expressed in anagen, the active growth phase of the hair cycle. It has been identified in key areas of the follicle, including:

• Epithelial stem cell regions
• Outer root sheath (ORS) keratinocytes

These are critical zones that drive hair growth. So when a protein is highly active here, it is likely playing a functional role.

How Blue Light Influences Hair Growth

Research using 453 nm blue light, a specific wavelength, has shown some really interesting effects on hair follicle biology:

• Increased CRY1 protein levels in keratinocytes and whole follicles
• Prolongation of the anagen growth phase
• Delayed transition into catagen, the regression phase
• Increased metabolic activity and proliferation in ORS cells at low doses

In simple terms, low dose blue light appears to support hair staying in the growth phase for longer.

CRY1 and Hair Cycle Control

When researchers manipulate CRY1 directly, the effects become even clearer.

Silencing CRY1 leads to:

• Earlier transition into catagen
• Reduced cell proliferation

Activating CRY1 using compounds like KL001 leads to:

• Prolonged anagen phase
• Increased expression of growth related genes

CRY1 also appears to regulate genes involved in:

• Cell cycle progression, for example CDK6
• Apoptosis, or programmed cell death

This supports the idea that CRY1 helps maintain a pro growth, anti regression environment within the follicle.

It Is Not Working Alone: OPN3 and Light Signalling

CRY1 does not act in isolation. Another protein called OPN3, a blue to green light sensitive opsin, is also involved.

Both CRY1 and OPN3 are expressed in ORS cells, and research shows:

• Knocking down either protein reduces cell proliferation
• Both are required for the full effect of blue light on hair growth

This suggests a coordinated light sensing system within the follicle, where multiple photoreceptors work together to influence growth and cell behaviour.

The Circadian Connection

One of the most interesting aspects of CRY1 is its link to the circadian rhythm.

Hair follicles appear to have their own clock system, involving genes like:

• BMAL1
• CLOCK
• PER1
• CRY1

These genes oscillate over a 24 hour cycle and are linked to:

• Timing of the hair growth phase
• Stem cell activity
• Cellular turnover

There is also evidence from animal models, such as seasonal hair growth in goats, showing that light exposure and photoperiod can influence hair cycling via these clock genes.

So this is not just about light hitting the skin. It is about light acting as a timing signal for hair growth itself.

What This Means for Treatments

From a practical perspective, this research opens the door to light based therapies for hair growth.

The key takeaways so far:

• Low dose blue light may enhance hair growth by increasing CRY1 activity
• CRY1 supports the anagen phase and reduces premature regression
• There is a clear biological mechanism, not just a cosmetic effect

However, this is important. Most of the current evidence comes from:

• In vitro, cell based studies
• Ex vivo, isolated human follicle models

We still need well designed human clinical trials to determine:

• Optimal wavelengths and dosages
• Safety over long term use
• Real world effectiveness

Take Home Message

CRY1 is emerging as a key regulator in hair follicle biology, linking light exposure, circadian rhythms, and hair growth.

The current evidence suggests:

• CRY1 is highly active in growing hair follicles
• Blue light at 453 nm increases CRY1 levels
• This helps prolong the growth phase and support proliferation
• CRY1 works alongside other photoreceptors like OPN3
• Light based therapies show potential but are not fully clinically established yet

From my perspective, this is a great example of where lifestyle, environment, and cellular biology all intersect. It also reinforces something I always come back to. Small, often overlooked factors like light exposure can have a much bigger impact on the body than we realise.

And as always, the key is staying evidence based while keeping an open mind as the research evolves.

Medical Disclaimer

This article is for educational purposes only and is based on current research evidence. It is not intended to replace medical advice, diagnosis, or treatment. If you are experiencing hair loss or any scalp condition, you should consult with a qualified healthcare professional or dermatologist before starting any new treatment, including light based therapies.