Introduction:

Sunscreens are an important component of the therapeutic armamentarium of a dermatologist, cosmetologist and aesthetician. With the ever increasing demands in the patients for a more cosmetically acceptable sunscreen with lesser frequencies of application and its safety issues being a concern the quest for an ideal continues. Selecting a sunscreen for a patient is an art and should not be practised as a blanket regime. This article focuses on the basics of the mechanism of action of sunscreens, the suggested selection criterias and basic principles that should be followed while making a choice for the best possible sunscreen for a patient.

Indications for use of sunscreens:

The primary function of a sunscreen is to prevent damage of the skin following exposure to ultraviolet radiations. The common indications for usage of sunscreens include cutaneous conditions like(1):

1. Sunburn

2. Freckling, discoloration

3. Photoaging

4. Skin cancer

5. Phototoxic/ photoallergic reactions

6. Photosensitivity diseases

– Polymorphous light eruption (290-365 nm)

– Solar urticaria (290-515 nm)

– Chronic actinic dermatitis (290 nm-visible)

– Persistent light reaction (290-400 nm)

– Lupus erythematosus (290-330 nm)

– Xeroderma pigmentosum (290-340 nm)

– Albinism

7. Photoaggravated dermatoses

8. Post-inflammatory hyperpigmentation (postprocedure)

Classification:

Sunscreens are classified into organic and inorganic sunscreens.

Basic definitions:

UVB sunburn protection factor is defined as the minimal erythema dose of photoprotected skin divided by the minimal erythema dose of unprotected skin. It is noteworthy that a sunscreen with an SPF of 15 blocks about 93% of UVB radiation, while one with an SPF of 30 blocks about 97% of UVB radiation (2).

The most commonly used UVA protection indice is the Boots star rating. In vitro measurement of the ratio of a product’s UVA (320-400 nm) absorbance over its UVB (290-320 nm) absorbance is used to calculate its Boots star rating.

Broad spectrum sunscreen: Critical wavelength > 370 nm AND UVA protection factor > 4 (1).

Water-resistant sunscreen: Maintains the label SPF value after two sequential immersions in water for 20 min (40 min)(1).

Very water-resistant sunscreen: Maintains the label SPF value after four sequential immersions in water for 20 min (80 min).

The application of sunscreen is important both in quantity and in frequency for maintaining its affectivity. The recommendations include every 3-4 hourly application of sunscreen over the sun exposed areas. It is worthwhile to repeat the application of sunscreens in cases of photosensitive and pigmentary disorders or in cases of sensitive skin. The exact amount of sunscreen required to be applied on the skin for optimal protection should be recommended by the manufacturer based on the method and quantity of the sunscreen formulation used for determination of the SPF(3). When using physical sunscreens, it is advisable not to rub them too hard as they work best on the surface of the skin. They leave the surface of the skin with a milky glaze which can be quite useful for gauging which skin areas you are covering and which one may have missed.

The quantity to be applied is determined by the tea spoon rule which states:

“Teaspoon rule”(4)

3 mL (slightly more than half a teaspoon)

• for each arm

• for the face and neck

6 mL (slightly more than a teaspoon)

• for each leg

• for the chest

• for the back

The choice of sunscreens is determined by various patient related factors, environmental factors and by the quality of a sunscreen itself.

The patient factors which need to be considered while administering the sunscreens include the following:

1.       Nature of disease/ skin condition– conditions like photosensitive dermatoses and pigmentary disorders would require a sunscreen with a higher SPF and substantivity than while recommending sunscreens to patients with skin tanning.

2.       Age of the patient– it is better to choose inorganic sunscreens in children less than ten years of age and better to choose chemical sunscreens for an older patient as the use of sunscreens in neonates and children still remain debatable.

3.       Affordability– newer sunscreens with both UVA and UVB filters with newer technologies like sunspheres, nanospheres and with a higher substantivity have a higher pricing thus increasing the cost burden on the patient. Choosing a sunscreen which a patient can afford and whilch serves to benefit the disease increases patient compliance

4.       Skin type– while selecting a sunscreen the skin type of the patient based on Fitzpatrick grading helps to determine the choice. Apart from this knowing the nature of the skin of patients as to dry or oily or sensitive helps in choosing the formulation. A gel or gel cream based formulation is preferred in cases of oily skin whereas a lotion is preferred in dry skin conditions

5.       Site of sunscreen application– Although sunscreens are applied on photoexposed areas it is worthwhile to divide the areas on the basis of cosmetic appeal of the sunscreen. For example a gel based or powder touch sunscreen would be of choice while choosing the face area whereas an oily formulation or physical blocker may be acceptable for the hands and feet. Dividing the areas and choosing sunscreens improves patient compliance and reduces cost burden on the patient.

6.       Cosmetic acceptability– sunscreens by default have an oily feel as the active ingredients are in an oily form, however newer formulations use various technologies to give a better texture to the preparations while maintaining Synergy between UV filters and photostability. This is of immense importance while prescribing sunscreens for cosmetic reasons.

7.       Ease of application– Patient compliance is a problem with respect to application as sunscreens demand to be reapplied frequently atleast every 3-4 hourly. Choosing a sunscreen which has a higher substantivity helps in reducing the frequency of application and thereby improving patient compliance.

8.       Nature of job/ work profile of the patient- a general idea regarding the nature of job of the patient is important as it gives a fair idea regarding the amount of sun exposure as well as the ease of application of sunscreens

Environmental factors:

The choice of sunscreens especially the formulation and SPF selection to a certain extent depends on the environmental condition. Choosing a gel based or cream based sunscreen is better in places of higher humidity whereas an oily formulation is preferable in cold and dry places. Sunscreens need to be applied every two hourly in places of higher altitude with a cooler climate than on the plains. Sunrays are the strongest between 9am -4pm, when it is worthwhile to avoid direct sun exposure, use physical barriers in combination with chemical sunscreens.

Sunscreens quality:

1.       Substantivity of the sunscreen- sunscreens that are long acting require less frequent application and may be used in patients who cannot apply sunscreens regularly.

2.       Texture of sunscreen- A sunscreen which has a powdery feel or a sheer touch or a dry touch is more cosmetically acceptable thereby making it easy to use on areas like face.

3.       Hypoallergenic properties- in cases of sensitive skin a sunscreen with least potential for irritation may be chosen like physical sunscreens as opposed to chemical sunscreens.

Conclusion:

Choosing a sunscreen is not anymore a blanket therapy in dermatology. It is an art which needs to be mastered by combining years of experience with patient handling and a thorough knowledge of the range of products available in the market. This article tries to summarize the practical points that need to be considered while selecting a sunscreen which aims at reducing the cost burden, improving compliance and increasing the aesthetic well-being in a patient.

References:

1.       Kaimal S, Abraham A. Sunscreens. Indian J Dermatol Venereol Leprol 2011;77:238-43.

2.       Draelos ZD. Compliance and sunscreens. Dermatol Clin 2006;24:101-4.

3.       More BD. Physical sunscreens: On the comeback trail. Indian J Dermatol Venereol Leprol 2007;73:80-5.

4.       Schneider J. The teaspoon rule of applying sunscreen. Arch Dermatol 2002;138:838-9.