There are several factors that can affect the effectiveness of sunscreen agents in protecting the skin from UV radiation:1. Sun Protection Factor SPF : The SPF rating of a sunscreen indicates its ability to protect the skin from UVB radiation, which is responsible for sunburn and skin cancer. Higher SPF values offer greater protection, but no sunscreen can block 100% of UV rays.2. Broad-spectrum protection: A sunscreen that offers broad-spectrum protection guards against both UVA and UVB radiation. UVA rays can cause premature skin aging, while UVB rays cause sunburn. Both types contribute to skin cancer risk.3. Application: Applying sunscreen correctly and in the right amount is crucial for effective protection. Most people do not apply enough sunscreen, which can reduce its effectiveness. It is recommended to use about one ounce a shot glass full of sunscreen for the entire body and to apply it 15-30 minutes before sun exposure.4. Reapplication: Sunscreen should be reapplied every two hours or immediately after swimming, sweating, or towel drying. Even water-resistant sunscreens can lose their effectiveness over time or when exposed to water.5. Expiration date: Sunscreen can lose its effectiveness over time, so it's important to check the expiration date and replace expired products.6. Storage: Sunscreen should be stored in a cool, dry place away from direct sunlight. Exposure to heat and sunlight can cause the active ingredients to break down, reducing the product's effectiveness.7. Skin type: Individuals with fair skin, light hair, and light eyes are more susceptible to sunburn and may require a higher SPF and more frequent reapplication.8. Environmental factors: The intensity of UV radiation can vary depending on factors such as altitude, latitude, time of day, and cloud cover. Sunscreen may be less effective in situations with intense UV exposure, such as at high altitudes or near the equator.9. Photostability: Some sunscreen ingredients can break down when exposed to sunlight, reducing their effectiveness. Look for sunscreens with photostable ingredients that maintain their protective properties when exposed to UV radiation.10. Interactions with other products: Some skincare products, such as certain acne medications, can increase skin sensitivity to sunlight. In these cases, it's essential to use a high SPF, broad-spectrum sunscreen and reapply frequently.