Sunscreen Chemistry: How It Protects Your Skin

Sunscreen is crucial for protecting your skin from the harmful effects of ultraviolet (UV) radiation. It helps prevent sunburn, skin cancer, and premature aging caused by sun exposure. Regular and proper use of sunscreen is essential for maintaining skin health and appearance at any age. But to understand how to use sunscreen we need to understand why to use it. And for that we need to understand UV rays.

Understanding UV radiation

There are 3 types of UV rays: UVA, UVB, UVC. The UVA and UVB rays reach the Earth surface while de UVC rays are absorbed by the atmosphere. UVA rays are long-wavelength and penetrate deeply, while UVB rays are medium-wavelength and cause sunburns and contribute to skin cancer.  

UVC:

While they don't pose a risk from natural sunlight, they can be harmful from artificial sources like special lamps or lasers. These rays have the shortest wavelengths and highest energy levels within the UV spectrum, and can cause severe damage to skin and eyes. 

UVB:

They only make up about 5% of the UV radiation reaching the Earth, they are high energy and can cause significant damage to the outer layers of the skin. UVB rays penetrate the epidermis (outermost layer of skin) and can cause sunburn, skin darkening and thickening, and DNA damage that can lead to melanoma and other skin cancers. 

UVA:

They penetrate the skin more deeply than UVB rays and are a significant factor in premature aging. UVA rays are responsible for tanning the skin, but there is no such thing as a safe tan, as tanning indicates skin damage. They also contribute to the development of skin cancer, including melanoma, basal cell carcinoma, and squamous cell carcinoma. UVA rays can penetrate clouds, so you're still exposed to them on cloudy or rainy days.


Active Ingredients in Sunscreen

Sunscreen formulations contain UV absorbing compounds (the active ingredients) dissolved or dispersed in a mixture of other ingredients, such as water, oils, moisturizers, and antioxidants. The UV filters can be either: organic or mineral.

Common UV filters include:

Avobenzone

Octocrylene

Octinoxate

Oxybenzone

- Organic

  • Avobenzone – absorbs UVA

  • Octinoxate and Octocrylene – absorb UVB

  • Oxybenzone – absorbs both UVA and UVB

    - Mineral

  • Zinc oxide (ZnO)

  • Titanium dioxide (TiO₂)

These minerals form a physical barrier, almost like tiny mirrors, bouncing UV rays away from the skin. They're especially good for sensitive skin and start working immediately after application.

Mechanism of Action

Sunscreen works by either absorbing, reflecting, or scattering UV radiation before it can penetrate the skin and cause cellular damage.

  • Chemical filters absorb high-energy UV rays and convert them into lower-energy heat through molecular excitation and relaxation. These filters contain bonds that absorb UV photons, preventing them from damaging skin cells and DNA.

  • Physical filters, like zinc oxide and titanium dioxide, act like tiny shields, reflecting and scattering UV radiation. This prevents most of the harmful rays from even reaching the skin surface.

The effectiveness of these mechanisms depends on how well the ingredients cover the UVA and UVB spectrum, as well as their ability to remain photostable under sunlight.

SPF and Broad-Spectrum Protection

SPF (Sun Protection Factor) refers specifically to UVB protection, which causes sunburn. For example:

  • SPF 15 blocks about 93% of UVB

  • SPF 30 blocks about 97%

  • SPF 50 blocks about 98%

However, SPF doesn’t measure UVA protection, which is responsible for deeper skin damage and aging. That’s why broad-spectrum sunscreens, which protect against both UVA and UVB, are essential. Higher SPF does not mean exponentially better protection, and no sunscreen blocks 100% of UV rays.


Formulation Chemistry

Sunscreen is more than just active ingredients — the overall formulation determines its stability, texture, and effectiveness.

  • Emulsions are the most common format: oil-in-water or water-in-oil mixtures that allow even distribution.

  • Stabilizers and antioxidants (like Vitamin E or BHT) are added to prevent the breakdown of sensitive ingredients, especially under UV exposure.

  • Film formers and water-resistant agents help the sunscreen stay on the skin longer, even when sweating or swimming.

  • Fragrance, preservatives, and moisturizers are also included but may cause irritation for some users with sensitive skin.

Chemistry ensures sunscreens are not only protective but also wearable, water-resistant, and cosmetically appealing.

Conclusion: The Chemistry of Prevention

Sunscreen is a powerful tool in modern skincare and public health, blending chemistry and dermatology to prevent both short-term and long-term skin damage.

  • It works through well-studied chemical and physical interactions that block harmful UV radiation.

  • Regular, proper use reduces the risk of skin cancer, premature aging, and sunburn.

  • Innovations in formulation continue to make sunscreens more effective, stable, and user-friendly.

In essence, sunscreen is a daily, science-backed shield — and understanding its chemistry helps us use it smarter and more effectively.


Next
Next

The Chemistry Behind Fireworks