By Elizabeth Rostan, MD

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Quick Look


Around age 30, our skin stops producing collagen. Aging and sun damage lead to collagen loss as well as loss of elastic tissue in our skin. Collagen can be thought of as the strength of our skin and elastin the stretch or rebound of our skin. This collagen and elastin loss continues and leads to fine lines, sagging skin, wrinkles, and texture changes.


Physical sunscreen WORKS LIKE A SHIELD; it sits on the surface of your skin, deflecting the sun’s rays.

UVShield e1631497244923

Chemical sunscreen WORKS AS A SPONGE; absorbing the sun’s rays.



Exposure to UV radiation increases your risk of skin cancer, and it’s estimated that about 80% of skin’s aging comes from the sun.

Sunbathing girl

Photo: Young Elizabeth Rostan

In my youth, I spent countless hours outdoors with almost no sunscreen. When I was a teen in the 80’s, getting that great tan was a primary goal – and a goal my friends and I worked hard on! In medical school, I had rotations in dermatology where I saw first hand the effects of too much sun.

As part of training, we also studied tissue under the microscope and believe me, if you see what the sun damage can do at a cellular level, it is enough to make you want to stay out of the sun! I began to learn also the cosmetic consequences of too much sun exposure – wrinkles, sagging skin and blotchy skin. Indeed, the changes of sun on our skin far outweigh the changes of aging.

So, in my early 20’s I began to change how I spent time in the sun and how I protected my skin.

Let me share what I now know and practice. In this blog series, we will review the sun and its effects on your skin, help explain SPF and how sunscreen works, and outline great sun protective behaviors for a lifetime of healthy skin.

The Sun and
Your Skin

Ultraviolet Rays

The sun emits ultraviolet radiation in 3 forms:

UVC is completely blocked by our atmosphere and does not reach earth. UVA is longer wavelengths and referred to as the “aging sun rays”. UVB rays are shorter wavelengths and called “sunburn rays” – but both can lead to skin cancer. Tanning beds can emit rays 10-15 times stronger than the sun.

Types of UV


The Sun Damages Skin?

DNA damage and skin cancer

UV rays from the sun damages DNA in skin cells. DNA makes up the genes that drive our cellular functions – life’s engine.

When DNA is damaged, genes in our cells are defective and some genes that cause growth can be turned on – causing cells to grow unchecked ie a tumor – while other important genes called suppressor genes that inhibit tumor growth may be turned off.

So, sun damages DNA causing some genes that drive tumor growth to be turned on indefinitely – the accelerator on life’s engine. At the same time, DNA damage leads to loss of tumor suppression genes – brakes don’t work. So accelerated, abnormal growth without any brakes – skin cancer.

Collagen Damage

Collagen and elastin make up the structure of our skin. UV exposure from the sun activates an enzyme called matrix metalloproteinase to be activated. When this enzyme is activated, it eats up the collagen in our skin.

There is a repair process but it is not perfect. The cycle is repeated with repeat sun exposure with more imperfect repair leading to collagen and elastin loss which leads to wrinkles and sagging skin.

Blotchy, imperfect skin

Repeat sun exposure stimulates pigment in the skin leading to numerous brown spots and blotches. Sun is also the biggest factor in creating unwanted redness and broken blood vessels.


A sunburn is an acute toxic reaction caused by too much exposure to the sun’s ultraviolet radiation. Typically it results in redness, swelling and tenderness initially and later peeling of the damaged skin. More severe cases can have blistering and even fever requiring medical treatment. Best to avoid sunburn.


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How much to apply

All these SPF numbers depend on properly applying sunscreen – which is a lot. The testing to determine SPF is based on applying 2 mg/cm2 – this translates to ¼ teaspoon for face alone (nickel size dollop) and 35 ml or a full shot glass for entire body. And then re-apply every 2 hours.

Thus, there is often a recommendation to use a higher SPF sunblock – say 30 or 50 – because too little is applied and an SPF 50 might become an SPF 30.



“I applied sunscreen in the morning so I should be set for the whole day.”

Sunscreens usually only last about 90-120 minutes, especially if you are using chemical blockers that breakdown after exposure to UV light. Always read the product instructions and reapply.


“I have a vitamin D deficiency, so I need more sun.”

Getting a tan does not increase your levels of Vitamin D. You you only need about 10 to 15 minutes of the sun daily before your body reaches maximum production of vitamin D and then it stops. The most efficient way is to have proper diet and sun moderation for healthy Vitamin D levels.


“I don’t need to wear SPF on a cloudy day.”

The clouds do not block the UV rays that can cause aging and skin cancer. It is important to always use your physical sunscreen even on cloudy days.


“I don’t use sunscreen because they are all oily and cause me to break out.”

Every sunscreen is not the same. Many products are absolutely more oily and can have preservatives that may cause allergic reactions, there is a large range of choices for skin from dry to oily. Look for products that have a clean finish of application and compact-based or even a mousse textured. You will need to do your research to found that perfect sunscreen.