Acne is basically a clogged pore which is either infected (a pimple ) or non-infected which is a whitehead or blackhead. Let's look the causes and how its formed.
How Acne Forms :
Stage 1 :
Dead Skin cells + Sticky Sebum ---> blocked pore
A clogged Pore (hair follicle). Your skin cells are constantly renewing, when old cells die they shed, And they reveal fresh skin but if your acne prone, sebum mixes with the dead skin cells, becomes sticky substance and block the pores.
Stage 2: Production of oil inside the pore. Normally the oil produced inside the port flows out through the 4 but since the pore is blocked the all stay inside. Androgen hormone stimulates oil production But during stress and puberty Androgen level is increased. Some oil is produced and the more blockage of what happens because of excess oil in dead skin cells and the oil which is produced inside build some pressure inside the pore.
Stage 3: bacteria p acnes which are naturally present in all skin types, Now have an abundant supply of food which is dead skin cells and Starts to breathe inside the Pore
Stage 4: Inflammation. The white blood cells rush to the area where there are excess bacteria and start fighting. This causes redness and swelling which is an actual pimple you see
As you have got the basic process of acne formation lets dive into the actual causes of acne.
Hormones
Androgen/ Testosterone- this hormone is linked to the oil production in the oil glands of the skin And shedding of dead skin cells. so when excess oil is produced and the skin cell not shed naturally the force can be blocked and then the formation of acne starts.
Cortisol or stress hormone make you produce excess oil in your skin. Stress in the short term might be gold to meet your deadlines but long-term stress can result in increased cortisol levels which will give you more acne
Insulin - Scientists have found that more insulin means more acne. Insulin spikes lead to over-keratinization, which means more dead skin cells, they stick to the surface and block pores. Also Insulin hugely increases your sebum production, actually a lot more than testosterone. Studies on diet and acne have found that low sugar and low GI diets reduce or even completely eradicate acne. So What are your blood sugar levels? Do they fluctuate? So to Be on the safe side take low glycemic index diet.
Genetics
Genes to some extent determine sebum production level and how skin responds to hormonal changes, stress, and inflammation. But there is no such thing as Acne Gene. So don't blame your genes but start working on things you can control like stress and hormones.
Oil and water balance in skin
Our sebum consists of both oil and water. When our skin is dehydrated (low levels of water in our skin), our skin tries to produce more sebum to compensate for the water loss. Hence more oil is produced which is not desired for acne-prone skin. So when you use a face wash / Soap / Cleanser which will strip all the oil and hydration from your skin, your skin produces more oil to compensate for the loss. So always choose a cleanser which is gentle on your skin.
Pollution & Environment
Heat - can increase oil production in the skin so more chances of breakouts. So during hot days, keep a facial tissue handy.
Humidity - In winter months there is low humidity and skin gets dry with low water levels, this will cause the skin to produce excess sebum( Combination of oil and water). This excess oil might cause you more breakouts. So it's important to keep your winter skin hydrated.
Sun exposure for short time might be helpful, as the blue band of light helps to sterilize the acne bacteria. But prolonged sun exposure oxidises you sebum, and increases the shedding of dead skin cells. This is a perfect scenario for pore to be blocked.
Sunscreens & Cosmetics
Sunscreens - Heavy sunblock's (Mineral sunscreens) have a lot of oil in them, which can block the pores. And chemical sunscreens work by absorbing UV light, which can increase the temperature in the inside the pore. This might again cause more acne. So your best option would be to go for small SPF. Many skin care experts agree that SPF 15-20 is more than enough. But apply every 3 hours if you are in out the sun. Maybe avoid long exposure to sun, exposing 30 min to sun 4 times a day is a lot less damaging than sun exposure for 2 continuous hours. Higher SPF usually contains very heavy oil or have a lot of sun filters which might increase the temperature inside the pore.
Coming to cosmetics, you use almond/olive oil on face, you are sure to get acne within 2 weeks. We all love natural cosmetics but creams heavy in a certain type of vegetable oils are sure to block your skin. Studies show that Oleic acid can be highly comedogenic. And oleic rich oils are Olive, Almond etc. So be sure to check if your face cream is rich in above oils. So keep those lovely natural creams to your body and use lightweight creams on the face.