On your site, you state that acne worsens at stage 4. Why is that? Is it normal to have acne in my upper back?
By the time you reach stage 4, your skin has fully developed your sweat and oil glands. The oil glands keep your skin flexible. Your sweat glands cool your body.
The problem is that growth produces a lot of heat, which leads you to sweat a lot. It does have some benefits. I’m sure you’ve noticed that you can go out without a jacket when older people are all bundled up. However, when the air is warm, produce a lot of sweat.
The rise in hormones that stimulate your growth also causes your oil glands to produce an abundance of oil for your skin. Perhaps you’ve noticed that young people’s skin looks smooth and soft. Older people’s skin is less flexible and drier. But during late stage 3 to early stage 5, you produce an over abundance of oil. Your skin is also still growing, which means dead skin cells are flaking off and clogging oil glands. If bacteria is also trapped under the clog, then an infection will set in, which is what acne is.
You can get acne anywhere you have skin. Because the soles of your hand and feet are thicker skinned, it is less likely to have acne. Your back can easily get acne and it is harder to wash the skin on your back to keep the oils down. Standing in a shower with hot water hitting your back does help a bit.