What is SPF?
SPF stands for Sun Protection Factor and is the system used worldwide to determine how much protection a sunscreen provides, applied to the skin at a thickness of 2 mg/cm2. The test works out how much UV radiation (mostly UVB) it takes to cause a barely detectable sunburn on a given person with and without sunscreen applied. For example, if it takes 10 minutes to burn without a sunscreen and 100 minutes to burn with a sunscreen, then the SPF of that sunscreen is 10 (100/10).

A sunscreen with a SPF of 15 provides >93% protection against UVB. Protection against UVB is increased to 97% with SPF of 30+. The difference between a SPF 15 and a SPF 30 sunscreen may not have a noticeable difference in actual use as the effectiveness of a sunscreen has more to do with how much of it is applied, how often it is applied, whether the person is sweating heavily or being exposed to water. Hence a sunscreen with SPF 15+ should provide adequate protection as long as it is being used correctly. However, most people apply their sunscreen at about one third the thickness used for testing; they fail to apply it to all exposed areas of skin; and they forget to reapply it every couple of hours. Therefore, the actual protection may be a lot less than the tests indicate.

Currently there is no internationally agreed test for measuring UVA protection in human skin. An estimate is made by a laboratory test in which the proportion of radiation passing through a measured amount of sunscreen is determined. To ensure some protection against UVA, products with physical blocking agents making up some of the active ingredients are recommended. http://dermnetnz.org/treatments/sunscreens.html

No sunscreen - no matter how high the factor - can offer 100 per cent protection.
Factor 15 sunscreen offers about 93% protection
Factor 30 sunscreen offers about 96% protection
Factor 60 sunscreen offers about 98% protection

What is PABA (Para-Aminobenzoic Acid)
What does it do? PABA is the abbreviation for para-aminobenzoic acid, a compound that is an essential nutrient for microorganisms and some animals, but has not been shown to be essential for people. PABA is considered by some to be a member of the vitamin B-complex, though its actions differ widely from other B vitamins. PABA has been reported to enhance the effects of cortisone.1 It may also prevent or even reverse accumulation of abnormal fibrous tissue.

What are the reactions to paraben mix allergy?
Paraben mix sensitivity produces classic allergic contact dermatitis reactions. Sometimes it may be seen as a flare or spread of an existing treated rash. Paraben allergic hypersensitivity is not uncommon although rare in relation to its widespread use. It appears that repeated applications of relatively low concentrations of parabens in medications and cosmetics may lead to sensitivity. Allergic reactions to orally ingested paraben-containing foods are rare.

What side effects may I notice from using PABA?
Side effects that you should report to your prescriber or health care professional as soon as possible:
•acne
•burning or itching of the skin
•dark red spots on the skin
•painful, red, pus-filled blisters in hair follicles
•pain in hairy areas

Side effects that usually do not require medical attention (report to your prescriber or health care professional if they continue or are bothersome):
•dry skin, irritation
http://www.drugdigest.org/DD/DVH/Uses/0,3915,7409%7CPara%252DAminobenzoic+Acid,00.html

The following advice as given on the Cancer Research UK website

There will always be times when we are out in the sun without adequate shade or cover-up clothing. This is when sunscreen is useful for protecting our exposed skin from the sun's rays. Sunscreen alone will not protect us completely from sun damage.

We should never use sunscreen in order to spend longer in the sun. It should be used to increase our protection.

Use factor 15+
The Sun Protection Factor (SPF) of a sunscreen is a measure of its ability to filter out dangerous UVB rays. The higher the factor the more protection you get from burning. But higher factor sunscreens tend to be more expensive.

Why factor 15?
The reason experts recommend factor 15, is that this represents the best balance between protection and price. You will get over 90 per cent protection from UVB rays with SPF 15. Above SPF 30 you don't get much additional protection from higher factors.

No sunscreen - no matter how high the factor - can offer 100 per cent protection.
Factor 15 sunscreen offers about 93% protection
Factor 30 sunscreen offers about 96% protection
Factor 60 sunscreen offers about 98% protection


Buying sunscreen
Choose one:

• With an SPF of 15 or above - this will give you over 90% protection

• Labelled 'broad spectrum' - to protect against UVA and UVB

• That is water resistant - it is less likely to wash or be sweated off

• With a valid 'use by' date - most sunscreens have a shelf life of 2-3 years

Do not store sunscreens in very hot places as extreme heat can ruin their protective chemicals.