Exposure to sunlight can lead to serious side effects ranging from sunburn to …

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Sunscreen to Protect From Sunlight by Clinical Pharmacist Dima Zeineddine

Sunscreen to Protect From Sunlight by Clinical Pharmacist Dima Zeineddine --KIMSHEALTH Oman Hospital


Exposure to sunlight can lead to serious side effects ranging from sunburn to premature aging and skin cancer.(https://www.kimshealth.om/specialities/dermatology/)

Ultraviolet A (UVA) represents 95% of the radiation reaching the earth, it penetrates deeply in the skin and contributes to photoaging and pigment darkening (https://www.kimshealth.om/specialities/dermatology/)

while Ultraviolet B (UVB), the more biologically active radiation, represents only 5 percent of the UV radiation, it damages the outermost layer of the skin and is responsible for sunburn, inflammation, hyperpigmentation, and photocarcinogenesis.

Sunscreens are topical preparations containing organic or inorganic (mineral) substances that reflect and scatter or absorb ultraviolet (UV) radiation in the (UVB) and (UVA) wavelength range. 

Broad spectrum sunscreens provide protection against both UVA and UVB.


1-SPF — The sun protection factor (SPF) value measures the level of protection against ultraviolet B (UVB) and ultraviolet A2 (UVA2) and is based on the ratio of the minimal erythema dose on sunscreen-protected skin compared with unprotected skin.

SPF = Minimum Erythma dose (with sunscreen)/Minimum Erythma dose (on unprotected skin)

SPF ratings consider both the amount of time you are exposed to UV radiation and the intensity of those rays.


2-The best SPF to use

Sunscreen products with SPF 15 are generally recommended for daily use. 

Broad-spectrum sunscreen products with SPF 30 or higher are recommended for individuals performing outdoor work, sports, or recreational activities.


3-Proper use of sunscreen

  • Apply sunscreen 15 to 30 minutes before sun exposure to allow the formation of a protective film on the skin and reapply every two hours.


  • Use the "Teaspoon rule" 

    •  Apply 1 teaspoon of sunscreen to the face and neck area

    • 2 teaspoons to the front and back torso

    • 1 teaspoon to each upper extremity and 2 teaspoons to each lower extremity


4-Water resistance  

Water (and sweat) resistant sunscreen should be considered while working or practicing sports or recreational activities outdoors.

The terms "water-resistant" and "very water-resistant" mean that the SPF is maintained after 40 or 80 minutes of activity in water or sweating, respectively.


5-Sunscreen suitable for each skin type 

For oily skin, Acne prone skin: use oil free, dry touch, anti-shine, fluid

For normal to oily skin: use fluid

For normal to dry skin: use cream, velvety cream

For sensitive skin: use hypoallergenic 


Good to know! 

The exposure to sunlight for one hour at 9:00 am results in the same amount of solar energy as 15 minutes at 1:00 pm


The SPF scale is not linear:

• SPF 15 blocks 93% of UVB rays
• SPF 30 blocks 97% of UVB rays
• SPF 50 blocks 98% of UVB rays



Summer has started already, patients must be aware to take their medicines correctly and store them properly.


Patients are advised to check their medications' side effects and follow instructions in the label carefully. Examples of medicines whose side effects can be intensified while practicing or working outdoor during summer time:

  • Diuretics can cause dehydration and affect kidney function.

  • Antihypertensive medicines can cause dizziness and fainting that can be dangerous when exercising in hot weather or when combined with a heat stroke.

  • Diabetic patients on insulin and oral antihypoglycemics must control their sugar level to avoid symptoms of hyper or hypoglycemia.( https://www.kimshealth.om/specialities/internal-medicine/

  • Laxative medicines can cause more loss of water and dehydration.

  • Antihistamine medicines can cause dry mouth. 

  • Antidepressants like selective serotonin reuptake inhibitors, or SSRIs, may increase sweating, increasing the risk of dehydration.

  • Others, like tricyclic antidepressants, or TCAs, may decrease sweating, making it harder to cool off.

  • Antipsychotics may impair sweating and alter the body’s internal thermostat.

  • Parkinson’s disease may interfere with sweating and the body’s internal thermostat. They may also reduce blood flow to the skin.

Therefore patients are advised to stay hydrated, exercise reasonably, preferably indoor and avoid  hot peak hours during the day.



  1. Store all medications in a cool dry place away from humidity at a temperature below 25 ˚C.

  2. Don’t store medications in the kitchen and Bathroom.

  3. Never keep medications in a closed car even for minutes. The temperature inside a closed car can rise up to 62 ˚C in one hour when the temperature is 38 ˚C outside.

  4. Be sure to take your medicines with you when you leave the car.

  5. Pack medications that need to be refrigerated in a small cooler with a frozen pack.


During summer, more precautions should be considered when taking drugs that induce photosensitivity reactions. These reactions can be either phototoxic or photoallergic.

Phototoxic reactions resemble sunburn and can progress to blistering.

They are dose dependent for both the drug and sunlight, occur within minutes to hours of taking the drug and subside quickly on drug withdrawal.

Phototoallergic rashes are usually eczematous but may be lichenoid, urticarial, bullous or purpuric. 

They are immune mediated, not dose dependent and occur following exposure to normal amounts of sunlight exposure. The onset can be delayed by weeks or months, while recovery is often slow following withdrawal.

Precaution measures to consider while prescribing photosensitive drugs:

  • Caution patients of the potential reaction for drugs considered to be potent photosensitizers and monitor.

  • Advise patients to avoid sun exposure.

  • If sun exposure is inevitable then implement secondary measures: apply sun protection upon treatment initiation, use of sun protective clothes and avoid sun during peak daylight hours.

  • Discontinue offending drugs once diagnosis of drug-induced photosensitivity is made and offer a treatment if necessary.


Common photosensitizing medications:

Antibiotics: Fluoroquinolones, tetracyclines, Trimethoprim

Antifungals: Itraconazole, Ketoconazole, Terbinafine, Voriconazole

Antimalarial: Chloroquine, Hydroxychloroquine, quinine

ACE inhibitors: Enalapril, Quinapril, Ramipril

ARBS: Candesrtan, telmisartan, Valsartan, Olmesartan, Losartan, Irbesartan

Diuretics: Furosemide, HCT, Indapamide

CCB: Amlodipine, Diltiazem, Nifedipine

Methyl dopa, Amiodarone, 

Lipid lowering agents: Atorvastatin, Simvastatin, Fenofibrate

Chemotherapy agents

NSAID: Celecoxib, Diclofenac, Indomethacin, Naproxen, Piroxicam

Antidepressant: Escitalopram, Fluoxetine, Paroxetine, venlafaxine, Haloperidol, Olanzapine, Risperidone, Alprazolam, 

Others: Clopidogrel, Carbamazepine, diphenhydramine, esomeprazole, ethinyl estradiol, glyburide, isotretinoin, leflunomide, mesalamine, Metformin, Sitagliptin, Pantoprazole

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