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November 22, 2009
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Sun-Sensitive Drugs
(Photosensitivity to Drugs)

Medical Author: Siamak Nabili, MD, MPH
Medical Editor: Melissa Conrad Stöppler, MD

Making Sense of Sunscreen Products

Medical Author: Melissa Conrad Stöppler, MD
Medical Editor: Barbara K. Hecht, PhD

Find out how to choose the best sunscreen.Most people are understandably confused when it comes to choosing a sunscreen because of the baffling array of available choices. Common questions about sunscreens include

  • How high should the SPF be?
  • Should it block UVA or UVB?
  • Does it matter whether it is a gel, cream, or spray?
  • Should it be water-resistant or waterproof?

SPF stands for sun protection factor. The SPF numbers on a product can range from as low as 2 to as high as 60. These numbers refer to the product's ability to screen or block out the sun's burning rays. The SPF rating is calculated by comparing the amount of time needed to produce sunburn on protected skin to the amount of time needed to cause a sunburn on unprotected skin. The higher the SPF, the greater the sun protection.

What is photosensitivity?

Photosensitivity (or sun sensitivity) is inflammation of the skin induced by the combination of sunlight and certain medications or substances. This causes redness (erythema) of the skin and may look similar to sunburn.

Generally, these reactions can be divided into two mechanisms, 1) phototoxic reactions and 2) photoallergic reactions. Phototoxic drugs are much more common than photoallergic drugs.

What is the difference between a photoallergic and a phototoxic reaction?

Phototoxic reactions

In phototoxic reactions, the drug may become activated by exposure to sunlight and cause damage to the skin. The skin's appearance resembles sunburn, and the process is generally acute (has a fast onset). Ultraviolet A (UVA) radiation is most commonly associated with phototoxicity, but ultraviolet B (UVB) and visible light may also contribute to this reaction.

A phototoxic reaction typically clears up once the drug is discontinued and has been cleared from the body, even after re-exposure to light.

Photoallergic reactions

In photoallergic reactions, the ultraviolet exposure changes the structure of the drug so that is seen by the body's immune system as an invader (antigen). The immune system initiates an allergic response and cause inflammation of the skin in the sun-exposed areas. These usually resemble eczema and are generally chronic (long-lasting). Many drugs in this family are topical drugs.

This type of photosensitivity may recur after sun exposure even after the drug has cleared from the system.

What is ultraviolet light?

Ultraviolet (UV) light is radiation energy in the form of invisible light waves. UV light is emitted by the sun and by tanning lamps.

The sun discharges three types of ultraviolet radiation:

  1. ultraviolet A (UV-A),

  2. ultraviolet B (UV-B), and

  3. ultraviolet C (UV-C).

Only UV-A and UV-B rays reach earth. (UV-C does not penetrate the earth's upper atmosphere.)

Tanning lamps also produce UV-A and/or UV-B. These artificial rays affect the skin in the same way as do UV-A and UV-B from the sun.



Next: What are the symptoms of sun sensitivity (photosensitivity)? »

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Sun-Sensitive Drugs (Photosensitivity to Drugs)

Introduction to heat exhaustion

Heat exhaustion is a milder form of heat-related illness that can develop after several days of exposure to high temperatures and inadequate or unbalanced replacement of fluids. Those most prone to heat exhaustion are elderly people, people with high blood pressure, and people working or exercising in a hot environment.

Heat exhaustion symptoms

Warning signs of heat exhaustion include:

  • heavy sweating
  • paleness
  • muscle cramps
  • tiredness
  • weakness
  • dizziness
  • headache
  • nausea or vomiting
  • fainting

The skin may be cool and moist. The victim's pulse rate will be fast and weak, and breathing will be fast and shallow. If heat exhaustion is untreated, it may progress to heat stroke, which is a medical emergency. Seek medical attention and call 911 immediately if:...

Read the Heat Exhaustion article »



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