Bioactive glass, composed of inorganic oxides such as SiO₂ (silicon dioxide), CaO (calcium
oxide), Na₂O (sodium oxide), and P₂O₅ (phosphorus pentoxide), is known for its unique
ability to interact with biological systems. Its bioactivity allows it to react with aqueous
solutions (such as human perspiration, humidity, or body fluids) and elicit a range of
beneficial biological effects. These effects make bioactive glass particularly valuable for
various cosmetic and dermatological applications.

Key Properties and Biological Effects of Bioactive Glass:

1. Anti-Microbial/Antibacterial Behaviour:
   Bioactive glass has been shown to exhibit antibacterial properties, helping to reduce the growth of harmful bacteria on the skin. This property makes it useful in formulations for acne treatment, wound care, and general skin hygiene
2. UV Screening:
   Bioactive glass can act as a physical UV filter, protecting the skin from harmful ultraviolet radiation. This makes it a valuable ingredient in sunscreens and other protective skincare products.
3. Anti-Inflammatory Action:
   The interaction of bioactive glass with biological fluids can also result in anti inflammatory effects. This is beneficial for soothing irritated or inflamed skin, making it ideal for use in products aimed at sensitive or reactive skin conditions.
4. Mineralogical Film Formation:
   When exposed to body fluids or moisture, bioactive glass can form a mineralized layer on the skin, which may aid in skin regeneration and barrier repair. This film can act as a protective shield, helping to lock in moisture and promote healing.
5. Therapeutic Release of Inorganic Ions:
   Bioactive glass slowly releases beneficial ions such as calcium, phosphate, and sodium when it comes into contact with moisture. These ions can support skin health by promoting hydration, aiding in cellular repair, and possibly stimulating collagen production.

Bioactive glass has promising potential as a sunscreen ingredient, primarily due to its unique ability to absorb UV light and form a mineral-rich precipitate on the skin’s surface that improves its sun-blocking effectiveness over time.

UV Absorption and Sun-Blocking Properties:

1. UV Absorption:
   Bioactive glass begins to absorb UV light at wavelengths below 380 nm. Notably, a 5 mm thick polished bioactive glass blank showed 0% transmittance for UV radiation with wavelengths below 280 nm. This suggests that bioactive glass is highly effective in blocking UVB radiation (270-320 nm), which is responsible for sunburn and skin damage.
2. Protection in the UVB Range:
   Bioactive glass is considered an excellent sunblock for UVB radiation (270-320 nm) because of its ability to absorb this wavelength range effectively. UVB rays are primarily responsible for causing skin burns, and blocking them is essential for preventing immediate skin damage.
3. Moderate Protection in the UVA Range:
   Bioactive glass provides moderate protection in the UVA range (320-400 nm), the longer wavelength radiation that contributes to skin aging and deeper skin damage. While the glass doesn’t block UVA as effectively as UVB, it still offers a reasonable level of protection in this range.

Time-Dependent Improvement in Sun-Blocking Effectiveness:

One of the most unique aspects of bioactive glass as a sunscreen ingredient is that its sunblocking effectiveness improves over time after application to the skin. This enhancement is driven by a chemical reaction between the bioactive glass and human perspiration (sweat).

1. Formation of a Porous, Mineral-Rich Precipitate:
   As bioactive glass reacts with human perspiration, it forms a porous precipitate at the surface of the glass. This precipitate is rich in hydroxyapatite (HAp), a mineral that is similar to the natural mineral content of bones and teeth, known for its ability to scatter light. Hydroxyapatite forms a protective layer on the skin that acts as a physical barrier to UV radiation.
2. Improvement in Sun-Blocking Characteristics:
   Over time, as the reaction continues and the Hydroxyapatite (Hap) rich precipitate forms, the scattering properties of the surface increase. The more porous and mineralrich this layer becomes, the better it scatters solar radiation, effectively improving the sun-blocking characteristics of the bioactive glass.
3. Active Sunscreen Ingredient:
   This dynamic, self-improving effect makes bioactive glass an active sunscreen ingredient. Unlike conventional sunscreens, which may degrade or lose efficacy over time, bioactive glass’s protective effects intensify with exposure to sweat. The porous mineral layer formed on the skin’s surface enhances both UV absorption and scattering, providing prolonged and possibly enhanced protection as time goes on.