Sunscreen Smarts: Why I Build a Solar Callus (and What I Use When I Don’t)
- Evelyn Andersen, APNP
- May 27
- 4 min read
Every summer, I get asked the same question: “What sunscreen do you recommend?”
And while I do have favorites (I’ll share those below), my answer always starts with this: The best sun protection is your own biology — when it’s working with the light, not against it.
Let’s Talk About the Solar Callus
Our skin was designed to interact with sunlight. When exposed to the sun consistently and intentionally — especially early in the season and early in the day — the body adapts. This process, often called building a solar callus, leads to thicker, more resilient skin, increased melanin production, and a natural defense against UV damage.
It’s similar to exercise — you wouldn’t run a marathon without conditioning your body first. The same goes for sun exposure. Gradual, daily exposure helps reduce the risk of sunburn while supporting overall skin health.
Circadian Rhythm + Sun Resilience
Your skin follows a circadian rhythm — it knows when to produce antioxidants, when to repair DNA damage, and when it’s most resilient. Aligning with your natural light-dark cycle strengthens your body’s ability to respond to sunlight appropriately.
To help patients build this rhythm, I recommend the MyCircadian App — an easy-to-use tool that helps track light exposure, meal timing, movement, and more. It’s an incredible resource for optimizing your biological clock, which in turn makes your skin more adaptive and sun-smart. With code: GMOFWI, you can access a free 3-week trial on Android or a 1-month trial on Apple. Plus, lifetime subscribers will receive a 10% discount on one-time payments.
But When Sunscreen Is Needed…
There are absolutely situations where sunscreen is helpful — extended outdoor time, high UV days, or when you’re still building your solar tolerance. But not all sunscreens are created equal. The goal is to choose products that protect without disrupting your hormones, microbiome, or skin barrier.
Here are my go-to non-toxic sunscreen options:
Primally Pure SPF Collection
A beautifully formulated line that checks every box: seed oil-free, mineral-based, and skin-nourishing.
What sets it apart:
100% mineral-based protection
Non-nano zinc oxide
No hormone-disrupting chemicals
Skin-loving ingredients like tallow and jojoba
Reef safe + microbiome friendly
No white cast — seriously
Kid-safe and gentle for sensitive skin
Products include:
Sun Cream SPF 30 – Lightweight and sheer for daily use on face + body
Sun Stick SPF 25 – Portable, smooth, and perfect for on-the-go reapplication
Sun Lip Balm SPF 15 – Nourishing and protective with a tallow base
Use code evelyn10 at checkout for 10% off at primallypure.com
Rowe Casa Sun Shield (Available in-office)
This natural balm blends non-nano zinc oxide with red raspberry seed oil, carrot seed oil, and shea butter — all rich in antioxidants and supportive of your skin barrier. It’s safe for sensitive skin, babies, and anyone wanting clean, effective protection. Available in clinic.
Agent Nateur SPF Line
A luxurious option that merges skincare and sun protection: If you’re looking for luxury meets performance, this line blends clinical-grade sun protection with the feel of high-end skincare.
Holi (soleil) - is a sheer, dew-enhancing skin protecting drop formulated with hydrating ingredients, antioxidants, and SPF 50+. protect against free radicals and blue light radiation
Holi (Sun) SPF 50 — a fluid, elegant, tinted sunscreen with zinc oxide, aloe, and hyaluronic acid; available in 4 different shades to best suit your skin tone. Protect against free radicals and over 35% of blue light radiation. Code: GREENAGENT for 22% off all Agent Nateur in the Green Medicine Store.
General Guidelines: When to Use Sunscreen Based on UV Index and Skin Type
The UV Index (UVI) is a global standard to estimate solar UV radiation levels. The higher the number, the greater the potential for skin damage. UV index is avaliable on the MyCircadian App
Your risk also varies based on your Fitzpatrick skin type:
Type I–II: Very fair to fair skin, burns easily
Type III–IV: Medium to olive skin, sometimes burns
Type V–VI: Brown to deep skin, rarely burns but still vulnerable to DNA damage
SPF Recommendations Based on Skin Type
Your skin’s natural melanin content plays a major role in how much sun protection you need. Fair skin types (Fitzpatrick I–II), which burn easily and tan minimally, should use a broad-spectrum SPF of at least 30 daily when UV index is moderate or higher — even with short outdoor exposure. Medium-toned skin (Types III–IV), which tans more easily, may not need daily sunscreen in low UV conditions but should still use SPF 30–50 when spending extended time in the sun. Darker skin types (Types V–VI), while more protected against visible burns, are still at risk for UV-induced DNA damage and hyperpigmentation, especially on thinner areas of the skin like the face. SPF 30 is still recommended during high UV exposure, even for those with deeply pigmented skin. Regardless of skin type, morning sun exposure without sunscreen can be beneficial for building a solar callus and supporting circadian rhythm — but intentional use of SPF later in the day helps strike the right balance between resilience and protection.
Final Thoughts
The sun is not something to fear — it’s something to build a healthy relationship with.
By syncing with natural light, supporting your circadian rhythm, and using clean SPF when needed, you’re working with your biology — not against it.
Need help getting started?
Download the MyCircadian App
Start your day with 10–15 minutes of morning sunlight
Choose non-toxic SPF when needed
And remember: light is information for your body
To light, alignment, and luminous skin,