@zaidkdahhaj: Sunbathing gets a lot of press...

Sunbathing gets a lot of press.

Some of us love it and understand its healing power through heliotherapy.

Others believe it’s the single most damaging, skin cancer causing activity.

I would argue that most people think of sunbathing as a reckless activity, one that leads to burns, wrinkles, and cancer. But that’s only true if you misunderstand how the human body was designed to interact with light.

The truth is this that your skin is not a passive surface. It’s an intelligent, light sensing organ governed by circadian mechanisms. When you follow the natural solar cycle.. starting with morning light, progressing to controlled midday UV exposure, and ending with total darkness at night.. you unlock a complete system of repair, resilience, and regeneration.

This article will be a masterclass in breaking down exactly how you should think about the practice of sunbathing, so that it has an incredible impact on your health and quality of life.

Sunbathing: A Hormetic Practice

It’s incredible how people haven’t realized we’re talking about hormesis through progressive overload. The same principles that make exercise healthy also make sunbathing healthy.

This is a fundamental paradigm shift most people miss:

Hormesis is the biological principle that small, controlled stressors make the body stronger, but only when applied progressively and with recovery.

When you lift weights, you don’t begin with 250 pound back squats. You build up. The stress tears muscle fibers, but it’s the recovery and adaptation that builds strength.

Sunlight works the same way.

You don’t go from a winter indoors to four hours in peak UV sun. You build a solar callus (a tan), slowly increasing exposure, starting with morning light, letting your skin adapt by producing melanin, urocanic acid, filaggrin, and antioxidants.

What the mainstream gets wrong is they treat sunlight like a poison, not a stimulus.

But in biology, dose and timing determine the outcome.

Too much too soon? Damage.

Right amount at the right time? Resilience.

Sunbathing isn’t reckless. It’s solar training. Just like working out, but for your mitochondria, skin, and circadian system.

The Solar Sequence Matters

The solar sequence (priming, training, and recovery) is foundational to how human circadian biology evolved in sync with the light and dark cycle.

Each phase entrains specific hormonal and cellular responses, and disrupting this flow (as modern society has done), is one of the root causes of modern chronic disease

Circadian disruption is the single greatest cause of chronic skin dysfunction, burns, and skin cancers.. which is why I often tell people that they should be worried about artificial light at night, altered light spectrums, and sun-avoidance rather than solar exposure.

Think of this sequence as three legs to a stool.

If you neglect any one of them, then you cease to have a functioning stool.

Prime in the Morning (The Warm-Up)

Morning sunbathing before UV manifests is the equivalent of a circadian warm-up.

It’s gentle, preparatory, and essential for priming the skin and circadian system through red and infrared light exposure, which make up about 80% of the total solar spectrum at this time before UV-A comes out.

I often say that the circadian principles are relatively straightforward, but the complexity within each of them is unfathomable, as I’ll show you below.

Morning sunlight stimulates the production of filaggrin, which then breaks down into urocanic acid, both of which play crucial roles in skin hydration and photoprotection.

Filaggrin is the skin’s structural and moisture retainer. It’s a protein that aggregates keratin fibers in the outermost layer of the skin. This aggregation is essential for forming a strong, resilient skin barrier that protects against environmental insults, pathogens, and physical damage.

After filaggrin has served its structural role, it is broken down into various components that contribute to the natural moisturizing factor. These components, which include free amino acids and their derivatives, are vital for retaining skin moisture, maintaining flexibility, and preventing dryness.

The production and processing of filaggrin are closely linked to the skin’s circadian rhythm and mechanisms. Morning sun exposure helps signal the skin to activate protective and reparative processes as the day begins, ensuring that the barrier is fortified before more intense UV exposure later in the day.

Urocanic acid is known as a dual role moisturizer and photoprotectant. Urocanic acid is one of the main breakdown products of filaggrin. Its presence is a direct indicator of the skin actively generating its natural moisturizing factors. As a component of the NMF, urocanic acid helps the skin to retain water, ensuring adequate hydration. Well-hydrated skin is less prone to irritation, cracking, and sensitivity, which is essential for overall skin health.

Urocanic acid also has a natural ability to absorb UV radiation. In its trans form, it helps to filter out UV, reducing the potential for DNA damage and contributing to the skin’s innate defense system. Some of the absorbed energy is transformed into the cis form, which, despite its acute immunomodulatory roles, still plays a part in the skin’s adaptation to UV exposure.

Morning UV-A exposure initiates melanocyte-stimulating hormone (MSH) release, which signals melanin synthesis. The midday benefit: more melanin means more UV absorption and dissipation as heat, reducing the risk of burns and oxidative stress.

Morning light (especially blue and red/infrared wavelengths) triggers Nrf2 and superoxide dismutase expression, master regulators of antioxidant response. The midday benefit is that these antioxidants neutralize reactive oxygen species generated by UV-B, preventing cellular and DNA damage.

Exposure to early AM sun induces photolyase and p53, enzymes that repair UV-induced DNA changes. This makes the body become more efficient at repairing any thymine dimers or “damage” from stronger UV-B.

Morning sunlight stimulates cholesterol sulfate production in the skin, a precursor to vitamin D3 synthesis. UV-B later converts 7-dehydrocholesterol into vitamin D3 more efficiently when skin is already metabolically primed.

Morning sunlight boosts dopamine and serotonin via retinal and dermal photoreception. This elevated mood, more parasympathetic tone, and less cortisol-driven inflammation allow the body to respond, not overreact, to UV exposure.

Light in the early day entrains PER and CRY circadian gene expression in skin cells. These rhythms control when cells divide, repair, and rest.. so UV exposure happens during the skin’s highest repair and protection window.

UV-A in morning releases nitric oxide from skin stores into circulation, which improves blood flow and vasodilation, which then helps thermoregulate during intense UV exposure, reducing inflammation and cellular stress.

Red and near-infrared light in morning sunlight stimulate cytochrome c oxidase in mitochondria, increasing ATP production and reducing oxidative stress. This makes mitochondria more energized and less prone to UV-induced dysfunction when preconditioned with early infrared light.

Morning sun exposure helps stabilize mast cells and balance histamine release through circadian tuning of immune cells, which reduces the chance of histamine-driven inflammation or skin sensitivity during UV intense hours.

Morning light supports sebocyte and ceramide activity, helping produce protective oils on the skin. This lipid layer offers additional UV buffering and prevents transepidermal water loss during heat and light stress.

Morning blue light suppresses melatonin temporarily, but it also resets the pineal clock to rebuild melatonin precursors (like serotonin) during the day. By nightfall, this leads to a higher circulatory melatonin surge, repairing any UV induced cellular damage via its antioxidant and mitophagy promoting effects.

AM light anchors the cortisol awakening response (CAR), peaking it early in the day. This keeps cortisol levels from spiking unpredictably later in the day, avoiding inflammatory overreactions to UV or heat.

Morning sun exposure gradually raises body temp and heat shock protein expression, which means you’re less likely to overheat, dehydrate, or suffer from UV induced stress when your thermoregulatory system is already online.

Sunlight in the morning calibrates immune cell trafficking (like neutrophils and T-cells), aligning their peak activity with daylight hours. UV induced immune responses (like inflammation or repair signaling) occur in rhythm, reducing collateral damage or misfiring.

This is just scratching the surface.

Morning sun isn’t optional, it’s the biological equivalent of a warm-up set.

Skip it, and you expose a cold, unprimed system to a potent stimulus.

Embrace it, and you unlock solar resilience.

Sunbathe During the Midday (The “Training Session”)

Once morning light has primed the system, the body is ready to receive the full hormetic stimulus of UV-A and UV-B. Both form of UV play a priceless role in maintaining your metabolic health.

This is the period where you actually build melanin.

As with any training session, you must be intentional, especially if you’re a novice who is lighter skinned in this realm. Refer to The Solar Callus Guide for a step by step breakdown.

https://zaidkdahhaj.substack.com/p/solarcallusguide

Vitamin D3 synthesis occurs through UV-B, which peaks during solar noon. This is the only window where vitamin D3 synthesis is efficient, especially for darker skin tones.

In essence, midday sun isn’t dangerous when it follows the circadian script. It’s the biological “workout” that strengthens your skin, immune system, and mitochondria.. training your cells through light, heat, and stress to become stronger, cleaner, and more adaptive.

The most important piece of advice I can give to you is the following:

This is a game of CONSISTENCY, not intensity.

We want to avoid going hard in the paint when we are unadapted, in the same way that you don’t want to jump into maximal sprints when you’ve never done so a day in your life. Slow and steady wins this game.

If all you can handle is five minutes of midday UV, that’s your limit. Rinse and repeat while progressively building up to more time within circadian alignment.

Make it Dark Once Nightfall Hits (The Recovery)

After priming and stimulus, the body needs deep, uninterrupted recovery in darkness to seal in the gains. This is the anabolic, regenerative part of the solar cycle. Most people do not know that the skin regenerates itself at NIGHT.

Learn more about the specifics here.

https://zaidkdahhaj.substack.com/p/your-skin-cant-heal-if-your-nights

Most live under bright, high LUX artificial light at night, which means they fail to give their skin barrier the darkness it desperately needs to regenerate appropriately.

Darkness isn’t just a game of sleep, it’s the activation of the body’s deepest repair systems, all orchestrated by endogenous circulatory melatonin. There’s more evidence than we know what to do with here.

When total darkness signals its release, circulatory (pineal) melatonin becomes a master antioxidant and mitochondrial healer, reversing UV induced damage, enhancing mitophagy, and activating detox pathways like NRF2.

During this time, skin regeneration peaks, with collagen synthesis and cell turnover driven by clock genes like PER1 and BMAL1. Critical antioxidants like glutathione and catalase are also recycled at night, preparing you for the next day's light exposure.

Meanwhile, leptin peaks, directing fat metabolism and fueling skin and immune recovery, but only if artificial light isn’t hijacking the signal. Inside the mitochondria, melatonin cools down oxidative stress and restores optimal energy flow.

Ultimately, circadian genes can only do their job if the light/dark cycle is respected.

Nighttime darkness isn’t optional.

It’s the phase that transforms solar stress into long term resilience.

The Full Circadian Skin Cycle

Each phase is irreplaceable.

If you skip any phase, you compromise the whole circadian system, which can then easily manifest in avoidable symptoms that people often blame the sun for such as hyperpigmentation, detoxification symptoms, and severe burns.

Morning sun without midday UV = no stimulus.

Midday UV without darkness = no repair.

Darkness without sunlight during the day = no hormetic signal to recover from.

To build truly resilient, rejuvenated skin, you must complete the circadian cycle.

There’s a lot more actionable circadian frameworks like this in my course

Shave 10-15 years off your learning curve towards mastery of metabolic health, sleep, sustainable and limitless energy, and so much more below

The course was made out of love and obsession, enjoy it and use it wisely

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