Step 1: COS Absorbs Harmful UV Light

Measurements confirmed that COS absorbs light across both UVA and UVB ranges.
➡ This means COS can help reduce the intensity of UV energy that penetrates the skin environment — not as a sunscreen, but as a supportive protective ingredient.

Step 2: COS Improves Cell Survival Under UVA

When fibroblasts were exposed to UVA (6 J/cm²), their survival rate dropped sharply. With COS treatment, however, cell viability increased in a dose-dependent manner.
➡ The more COS was present, the better the cells endured UV stress.

Step 3: COS Shows No Phototoxicity

Safety was carefully assessed. Unlike retinoic acid (which showed phototoxicity at 2 µM), COS did not produce toxic effects under UVA conditions.
➡ This underscores COS’s profile as a safe, biocompatible material.

Step 4: COS Preserves Healthy Cell Structure

Under a microscope, untreated UVA-exposed cells appeared irregular and stressed. With COS, fibroblasts retained their normal, elongated shape, reflecting better resilience.
➡ This suggests COS helps maintain healthy morphology and function even after UV damage.

Step 5: COS Reduces Collagen-Damaging Enzymes

UVA is known to trigger MMP enzymes (MMP-1, MMP-8, MMP-13), which break down collagen. COS treatment significantly reduced the secretion of these enzymes compared with untreated cells.
➡ Less MMP activity means slower collagen breakdown.

Step 6: COS Supports Natural Enzyme Inhibitors

Our bodies naturally regulate MMPs using TIMPs (tissue inhibitors of metalloproteinases). UVA reduced TIMP expression, but COS restored TIMP-1 and TIMP-2 levels.
➡ This dual action — lowering MMPs and raising TIMPs — helps protect collagen more effectively.

Step 7: COS Boosts Collagen Markers

Lab assays showed that COS increased expression of collagen types I, III, and IV, and restored procollagen levels that had been suppressed by UVA.
➡ Beyond slowing collagen loss, COS actively supports new collagen production.

Step 8: COS Regulates the AP-1 Pathway

AP-1 is a key signaling pathway activated by UV stress. It drives collagen breakdown by boosting MMPs and reducing synthesis. COS treatment down-regulated AP-1 activity, calming this destructive cycle.
➡ With AP-1 reduced, fibroblasts could focus on repair and balance instead of stress response.

Bringing the Results Together

When viewed as a whole, the findings are consistent and compelling:

• UV absorption: COS naturally filters harmful rays.

• Cell protection: COS increases survival and preserves healthy structure.

• Safety: No phototoxicity observed in the tested range.

• Enzyme control: COS reduces MMPs while boosting TIMPs.

• Collagen support: COS enhances collagen I, III, IV, and restores procollagen.

• Pathway balance: COS down-regulates AP-1 to stabilize cellular responses.

At Chitosan Global, we highlight these in-vitro results as strong scientific evidence that 3–5 kDa COS is a promising cosmetic active for skin exposed to photo-stress. While the data comes from laboratory models and not clinical trials, it paints a clear picture of how COS can contribute to healthier, more resilient skin when formulated into cosmetic products.

In the lab, 3–5 kDa COS demonstrated a rare combination of strengths: absorbing UV, protecting cells, reducing collagen loss, and supporting new collagen production — all without phototoxicity. This multi-level action is why we, at Chitosan Global, believe COS deserves attention as a next-generation ingredient for skin care innovation.