Sun protection – classification of sunscreens and SPF concept MCQs With Answer

Sun protection is a core topic for B. Pharm students, covering classification of sunscreens, the Sun Protection Factor (SPF) concept, and formulation considerations. Understanding organic (chemical) and inorganic (physical) UV filters, their absorption spectra, mechanisms against UVA and UVB, photostability, and safety profiles is essential for rational product design. Key regulatory and testing concepts — in vivo and in vitro SPF determination, critical wavelength, water resistance, and labeling requirements — influence clinical effectiveness and patient counseling. Knowledge of adverse effects like photoallergy, phototoxicity, and interactions with excipients or actives helps ensure safe use. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What does SPF (Sun Protection Factor) primarily measure?

• Protection against UVA-induced photoaging
• Ratio of minimal erythemal dose (MED) with sunscreen to MED without sunscreen
• Percentage reduction of UVB transmission through cloth
• Amount of visible light blocked by the product

Correct Answer: Ratio of minimal erythemal dose (MED) with sunscreen to MED without sunscreen

Q2. Which wavelength range is primarily responsible for sunburn (erythema) and is the main target of SPF?

• UVC (100–280 nm)
• UVA (320–400 nm)
• UVB (280–320 nm)
• Visible light (400–700 nm)

Correct Answer: UVB (280–320 nm)

Q3. Which parameter defines ‘broad-spectrum’ efficacy in many regulatory systems?

• SPF value greater than 50
• Critical wavelength ≥ 370 nm
• In vitro UVA-PF > 1
• Water resistance for 80 minutes

Correct Answer: Critical wavelength ≥ 370 nm

Q4. Which ingredient is an inorganic (physical) UV filter commonly used in sunscreens?

• Avobenzone
• Octocrylene
• Zinc oxide
• Homosalate

Correct Answer: Zinc oxide

Q5. Avobenzone is effective primarily against which part of the UV spectrum?

• UVC only
• UVB only
• UVA (especially long-wave UVA)
• Visible light

Correct Answer: UVA (especially long-wave UVA)

Q6. Which statement about photostability of organic filters is correct?

• All organic filters are inherently photostable and do not degrade
• Photostability is irrelevant for UVA protection
• Some organic filters like avobenzone require stabilizers (e.g., octocrylene) to maintain efficacy
• Photodegradation always increases SPF

Correct Answer: Some organic filters like avobenzone require stabilizers (e.g., octocrylene) to maintain efficacy

Q7. Which testing method is considered the gold standard for determining SPF for labeling?

• In vitro spectrophotometric absorbance only
• In vivo human subject MED determination
• Animal testing on mice
• Calculations from ingredient concentrations

Correct Answer: In vivo human subject MED determination

Q8. When applying sunscreen to achieve labeled SPF, what application density is specified in standard SPF testing?

• 0.5 mg/cm²
• 1.0 mg/cm²
• 2.0 mg/cm²
• 4.0 mg/cm²

Correct Answer: 2.0 mg/cm²

Q9. Which of the following best describes the mechanism of action of inorganic filters like titanium dioxide?

• They chemically react with DNA to prevent mutation
• They absorb UV and convert it into heat only
• They scatter and absorb UV radiation, providing physical blocking
• They inhibit melanin synthesis

Correct Answer: They scatter and absorb UV radiation, providing physical blocking

Q10. Which filter has been historically associated with PABA-related allergic reactions?

• Octisalate
• Para-aminobenzoic acid (PABA)
• Mexoryl SX
• Titanium dioxide

Correct Answer: Para-aminobenzoic acid (PABA)

Q11. Water resistance claims on sunscreen labels (e.g., 40 or 80 minutes) are based on:

• In vivo tests combining water immersion and standardized reapplication intervals
• Manufacturer estimates without testing
• In vitro water solubility measurements
• SPF measured after 24 hours

Correct Answer: In vivo tests combining water immersion and standardized reapplication intervals

Q12. Which of the following combinations is commonly used to stabilize avobenzone’s UVA activity?

• Avobenzone + PABA
• Avobenzone + Octocrylene
• Avobenzone + Zinc oxide
• Avobenzone + Titanium dioxide

Correct Answer: Avobenzone + Octocrylene

Q13. Critical wavelength is defined as the wavelength below which what percentage of the area under the absorbance curve occurs?

• 50%
• 85%
• 90%
• 95%

Correct Answer: 90%

Q14. Which sunscreen active is known for broad UVA protection and is often used in Europe (trade name Mexoryl)?

• Homosalate
• Mexoryl SX (ecamsule)
• Octisalate
• Avobenzone

Correct Answer: Mexoryl SX (ecamsule)

Q15. SPF 30 compared to SPF 15 roughly allows what percentage of UVB transmission?

• SPF 30 allows more UVB than SPF 15
• SPF 15 allows about 6.7% transmission while SPF 30 allows about 3.3% transmission
• Both allow 0% UVB transmission
• SPF values cannot be related to percentage transmission

Correct Answer: SPF 15 allows about 6.7% transmission while SPF 30 allows about 3.3% transmission

Q16. Which adverse effect is most commonly associated with chemical sunscreens rather than physical sunscreens?

• Immediate mechanical irritation
• Allergic contact dermatitis or photoallergy
• Permanent staining of clothing
• Systemic infection

Correct Answer: Allergic contact dermatitis or photoallergy

Q17. In formulation, why are solvents and emulsifiers critical for organic sunscreen performance?

• They have no effect on UV absorption
• They ensure homogeneous distribution, influence film formation, and can affect photostability and SPF
• They increase the molecular weight of filters
• They convert inorganic filters into organic ones

Correct Answer: They ensure homogeneous distribution, influence film formation, and can affect photostability and SPF

Q18. What is Persistent Pigment Darkening (PPD) used to assess?

• UVB protection only
• UVA protection effectiveness
• Water resistance
• Phototoxic potential

Correct Answer: UVA protection effectiveness

Q19. Nanoparticles of zinc oxide or titanium dioxide are used in sunscreens primarily to:

• Increase systemic absorption
• Improve transparency on skin while retaining UV protection
• Reduce SPF dramatically
• Act as preservatives

Correct Answer: Improve transparency on skin while retaining UV protection

Q20. Which factor reduces the effective SPF of a sunscreen in everyday use compared to standardized testing?

• Applying at 2 mg/cm² exactly
• Underapplication (less than recommended amount) and uneven coverage
• Using water-resistant formulations properly
• Formulations baked onto clothing

Correct Answer: Underapplication (less than recommended amount) and uneven coverage

Q21. Sunscreen labeling that lists SPF 50+ indicates:

• Exact SPF is 50.0 for sure
• SPF is at least 50 and may be higher; regulatory cap applied
• Only UVA protection is provided
• Product is ineffective against UVB

Correct Answer: SPF is at least 50 and may be higher; regulatory cap applied

Q22. Which of the following is a correct statement about in vitro SPF testing?

• In vitro always replaces in vivo and gives identical SPF values
• In vitro methods use spectrophotometric measurements on a substrate and are useful for screening but may differ from in vivo results
• In vitro testing measures only water resistance
• In vitro testing is performed on volunteers’ skin

Correct Answer: In vitro methods use spectrophotometric measurements on a substrate and are useful for screening but may differ from in vivo results

Q23. Which excipient can increase the penetration of some organic UV filters into the stratum corneum?

• High molecular weight polymer
• Penetration enhancers like propylene glycol or ethanol
• Inert pigments like titanium dioxide
• Gelling agents that form a rigid film

Correct Answer: Penetration enhancers like propylene glycol or ethanol

Q24. Photoallergic reactions to sunscreens are most closely associated with which mechanism?

• Immediate IgE-mediated response
• Delayed-type hypersensitivity triggered by photoproducts formed after UV exposure
• Direct cytotoxicity to keratinocytes
• Antimicrobial contamination

Correct Answer: Delayed-type hypersensitivity triggered by photoproducts formed after UV exposure

Q25. Which combination of filters provides complementary UVB and UVA coverage commonly used in modern broad-spectrum sunscreens?

• Homosalate (UVB) + Avobenzone (UVA)
• PABA (UVA) + Zinc oxide (visible light)
• Octinoxate (UVA) + Titanium dioxide (infrared)
• Water only + Glycerin

Correct Answer: Homosalate (UVB) + Avobenzone (UVA)

Q26. Which regulatory concept requires labeling if a product is intended to prevent sunburn and provide SPF claims?

• Treating sunscreen as a cosmetic with no regulation
• Treating sunscreen as an over-the-counter (OTC) drug or regulated sunscreen, depending on jurisdiction
• Classifying it as a food supplement
• Allowing any claim without evidence

Correct Answer: Treating sunscreen as an over-the-counter (OTC) drug or regulated sunscreen, depending on jurisdiction

Q27. Which photochemical event is most directly responsible for DNA damage leading to mutagenesis after UV exposure?

• Formation of cyclobutane pyrimidine dimers (CPDs)
• Protein denaturation only
• Increase in vitamin D synthesis
• Reduction of melanin content

Correct Answer: Formation of cyclobutane pyrimidine dimers (CPDs)

Q28. If a sunscreen has high SPF but poor UVA protection, which long-term risk remains inadequately addressed?

• Short-term sunburn only
• UVA-driven photoaging and some forms of photo-induced DNA damage contributing to skin cancer
• Protection against bacterial infections
• Hydration of the stratum corneum

Correct Answer: UVA-driven photoaging and some forms of photo-induced DNA damage contributing to skin cancer

Q29. Which approach can improve the overall photoprotection in a topical product?

• Using a single UV filter at low concentration
• Combining multiple filters with complementary spectra and adding antioxidants to reduce reactive oxygen species
• Removing all emulsifiers
• Relying solely on visible-light absorbers

Correct Answer: Combining multiple filters with complementary spectra and adding antioxidants to reduce reactive oxygen species

Q30. For patient counseling, which instruction most accurately improves real-world sunscreen effectiveness?

• Apply a thin layer once in the morning and never reapply
• Apply liberally (~2 mg/cm² equivalent), reapply every 2 hours or after swimming/sweating, and use additional measures (clothing, shade)
• Only apply sunscreen on cloudy days
• Use sunscreen only on weekends

Correct Answer: Apply liberally (~2 mg/cm² equivalent), reapply every 2 hours or after swimming/sweating, and use additional measures (clothing, shade)

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