1. What is SPF?

SPF (Sun Protection Factor) measures how well a sunscreen protects against UVB rays, which are primarily responsible for sunburn and contribute to skin cancer. It indicates how much longer you can stay in the sun without burning compared to unprotected skin.

2. How Does the Calculator Work?

The calculator uses the SPF formula:

Where:

• UV exposure time with sunscreen — Time in minutes until skin reddens with sunscreen
• UV exposure time without sunscreen — Time in minutes until skin reddens without protection

Explanation: SPF is a ratio comparing the time needed to produce sunburn with and without sunscreen protection.

3. Importance of SPF Calculation

Details: Understanding SPF helps choose appropriate sun protection and estimate safe sun exposure duration. Higher SPF values indicate greater protection against UVB radiation.

4. Using the Calculator

Tips: Enter the time until skin reddens with and without sunscreen in minutes. Both values must be positive numbers.

5. Frequently Asked Questions (FAQ)

Q1: What SPF should I use?
A: Dermatologists generally recommend SPF 30 or higher for adequate protection. SPF 30 blocks about 97% of UVB rays.

Q2: Does higher SPF mean proportionally more protection?
A: No. SPF 30 blocks 97% of UVB, SPF 50 blocks 98%, and SPF 100 blocks 99%. No sunscreen blocks 100% of UV rays.

Q3: How often should sunscreen be reapplied?
A: Every 2 hours, or immediately after swimming, sweating, or towel drying, regardless of SPF.

Q4: Does SPF measure protection against UVA rays?
A: No, SPF only measures UVB protection. Look for "broad spectrum" on labels for UVA protection.

Q5: Can I stay longer in the sun with higher SPF?
A: While higher SPF offers more protection, no sunscreen provides complete protection, and other factors like application thickness and skin type affect actual protection.