Choosing sunscreen - essentials things to know.

When you buy a sunscreen product, it is often influenced by the suggestions you get from your family and friends or some product advertisements. However, unlike many other things choosing a sunscreen is more of a medical decision rather than a cosmetic one because ideally your choice of sunscreen should be based on some complex factors. In the following sections we will try break it down into some easily understandable points.

Let’s start from the beginning. The sunlight we can see is only the visible part of it. But it has an invisible part which we call ultraviolet or UV rays. UV rays are usually responsible for all kinds of damaging effects that sunlight might have on our skin ranging from simple sun allergy to skin cancer. However, UV ray is not one single component rather it is like a spectrum and can be divided into 3 parts.

1. UV A ray : Mostly responsible for photo aging (wrinkles that makes the skin look old) and tanning in dark skin. Look for “PA rating” in your product label to verify that it has adequate UVA protection. Your product should have atleast PA rating 3+ and if it is 4+ then it’s excellent.
2. UV B ray : Mostly responsible for sunburn and skin cancers. You can look for SPF rating (Sun protection Factor) in your product label to confirm how much UVB protection does it offer.

In simple math, the amount of sun protection is 100 x ( 1 - 1/SPF) % . For example, when SPF is 50, the amount of sun protection is 100 x (1 - 1/50) = 98%, whereas for SPF 15, the sun protection is 100 x (1 - 1/15) = 93%. So you can see the difference is not as big as it looks.

However, if you are staying outside for long, minimum SPF 30 is recommended. And if you have a skin condition that might turn worse because of sun exposure, SPF 50 or above is preferable. 

Apart from UVA and UVB , there is also a UVC spectrum but we usually do not worry about it as it gets absorbed by the ozone layer of our upper atmosphere.

So your sunscreen should give you protection from both UVA and UVB part of the UV rays. 

Key Takeaway : look for both SPF and PA ratings

If you have a definitive skin condition that gets aggravated by sun exposure (such as melasma), you might need protection from visible light and heat (infra-red spectrum) as well. There are certain specific physical sunscreens that can offer you that. However, it is best to let your dermatologist assess if you need that or not.

This difference is based on how your sunscreen actually works.

1. Physical or inorganic sunscreen usually forms a complete layer outside your skin that blocks the uv rays mechanically. Zinc oxide or titanium oxide are examples of physical sun blocking agents. 
2. Chemical or organic sunscreen actually enters inside your skin. When Uv rays come they can absorb the uv ray themselves thereby protecting the skin cells. Examples of chemical sun blocking agents are avobenzone , octinoxate etc.

Also note that a single sunscreen product can have both physical and chemical sun blocking agents.

We usually prefer physical sunscreen due to some very specific reasons.

1. Chemical sunscreens might cause irritation and different types of sun allergies. Often patients complain that after applying sunscreen their face has turned darker. It is because of the chemical components.
2. Some chemical compounds have been outright banned in many countries because of their harmful potential (even some of them are thought to cause cancer ) like oxybenzone, octinoxate and benzophenone-3. 
3. Protection offered by chemical sunscreen are often incomplete as each chemical only absorbs a part of the UV spectrum and that too not uniformly. So manufacturers must combine multiple chemicals to achieve a complete protection. However, it is often not complete whereas physical sunscreens offer full protection against the whole UV spectrum.
4. Though not proven in studies, some people worry that chemicals might get absorbed into the body specially if applied over a large area.

The only downside of using a physical sunscreen is that they are usually more costly. But if you look at the benefits, it's well worth it.

Key takeaway : Try to choose a sunscreen with physical sunblocking agents.

This one is pretty straightforward. Oil based sunscreens are not suitable if your skin is oily or you often get pimple breakout. Water based sunscreen is usually preferred even in the dry skin where you can easily combine it with a moisturizer if needed. Oil based sunscreens also causes more sweating causing skin irritation and also washes the sunscreen away.

Sometimes you will hear a term “matte finish” to describe a sunscreen product. It means that it will blend very well with your skin and no uneasy sticky sensation will be felt. 

Key takeaway : Avoid oily sunscreen lotions specially if you have an oily skin

Certain few other things we suggest you take into account while choosing a sunscreen product.

1. Certain sunscreens contain products which can cause acne. You need to make sure that your sunscreen does not contain any comedogenic substance. Here is a list of comedogenic substances commonly found in various cosmetic products.
2. If you are a swimmer, prefer a water-proof sunscreen. The definition of water-proof sunscreen is a sunscreen that can sustain itself when your face is in contact with water for 80 minutes. For water-resistant sunscreen the time is 40 minutes. This is also relevant if you work in a hot and humid condition that makes you sweat more than usual.
3. If you have a sensitive skin, make sure your sunscreen does not contain any allergic substances. Some common allergic substances present in cosmetics are parabens and perfume. You can search for any ingredients here to discover if it has got any allergic (or other harmful) nature.
4. Also pay attention to its vehicle. Lotion is good for a large area (when you are going to take a sunbath), spray is good for kids , gel is preferred for oily skin and cream is good for dry or mixed skin type.
5. If your sunscreen has another component for some other purpose, it can be considered as an advantage. For example some sunscreen contains additional skin brightening agents or anti-oxidants.

Sunscreens should be used 15-20 minutes prior to expected sun or heat exposure (going outdoors or going to the kitchen). The application should be thorough and should cover all areas which are exposed to sun.

If you are being exposed to sun intermittently , for example your work consists of both desk jobs and sometimes you need to step up outdoors , you should use sunscreen every 2 hours. On the other hand if your work is continuously under the sun (any type of field work) , you need to reapply sunscreen every hour.

Recently there has been a debate regarding use of sunscreen and vitamin D synthesis as that requires exposure to UV rays. The current consensus among scientists is that you can safely continue to use sunscreen without any worry. If you however have a pre-existing vitamin D deficiency , you might consider vitamin D supplements or as instructed by your physician. 

So , to sum up you should use a sunscreen which is broad spectrum , preferably water based , non-comedogenic and mainly contains physical blocking agents. However, if you have sensitive skin , acne or any other skin problems, it is better to see a dermatologist before choosing a sunscreen (also some sunscreens they prescribe are usually available only in pharmacies as they are of medical grade).