As mentioned, the development of primary and secondary sexual characteristics begins during puberty and is brought about by the increase of certain hormones. This hormonal increase triggers many other changes as well. For instance, most teens will notice that their perspiration becomes more odoriferous which can be quite unpleasant. While most people believe that the perspiration itself is the cause of this unpleasant odor, it's actually bacteria feeding on the perspiration that create the unpleasant odor.
Interestingly, perspiration arises from two different types of glands: the eccrine glands and the apocrine glands. When most people think of perspiration, they typically think of a hot summer day, or a strenuous workout. This type of perspiration is caused by the body becoming too warm. To correct for this, the body begins to perspire to cool down. Perspiration coats the skin with moisture and creates a cooling effect. This enables the body to maintain a safe, core body temperature (approximately 98.6 degrees Fahrenheit/37 degrees Celsius). This type of perspiration is produced by the eccrine glands. These sweat glands are found all over the body and open directly onto the skin's surface. The sweat that is produced from these glands is composed of mostly water and salts. Bacteria don't grow very well in this type of sweat because salt inhibits the growth of bacteria. Therefore the sweat that comes from these glands is odorless. Since this protective cooling function is essential regardless of size or age, both children and adults produce this type of odor-free perspiration.
However, during puberty teens also begin to perspire from the apocrine glands. Unlike the eccrine glands which are found all over the body, these glands are found within hair follicles, so there are more of these sweat glands in places like the scalp, underarms, and groin, where hair follicles are grouped more closely together. These glands become activated during emotional responses such as excitement, happiness, fear, worry, and anger. The sweat produced by the apocrine glands is milky in appearance, and is loaded with many different substances that provide food for bacteria to grow. In addition to food, bacteria need a dark, moist climate in order to survive. Therefore, the underarms, groin, and scalp where hair is concentrated, provide the ideal climate for the growth of bacteria. It is these bacteria that put off the offensive odor that people associate with perspiration. Daily bathing removes both the bacteria and its food source.
Acne and oily skin
Hormonal changes can also cause skin problems by increasing the production of skin oil (sebum) and creating a greasier look and feel to the skin. Most teens struggle with acne blemishes at some point during their adolescent period. Acne blemishes are caused when the pores in the skin become blocked with this oil, or sebum, along with dead skin cells and other dirt or chemicals. However, it is less clear what causes the pores to become clogged in the first place. Some medical professionals believe the increased oil production is responsible for causing adolescent acne. However, other medical professionals believe the hormonal changes also cause the pores to become blocked more easily. Thus, doctors and scientists are not yet in agreement about the exact cause of adolescent acne.
Acne can appear anywhere on the body, but it most frequently occurs on the face, neck, back, chest, and shoulders. While people talk about acne or "pimples," there are actually six different types of common acne blemishes: whiteheads, blackheads, papules, pustules, nodules, and cysts.
Whiteheads are clogged pores that remain under the skin. While they are visibly noticeable, they do not swell or become red, so they are rarely painful. They appear "white" because they're under the skin surface.
Blackheads are also clogged pores that rarely swell or redden. However, these blemishes appear on the surface of the skin, so the pore blockage is visible and looks "black." The substance inside is not dirt, even though it can look like it.
Papules are blemishes that do swell a bit and feel tender. They are often pink in color.
Pustules are blemishes that are very obviously red and swollen. They will also have a layer of yellow pus at the top of the pimple.
Nodules are blemishes deep down under the skin. They will feel like very hard lumps under the skin and can be very painful. However, they rarely cause a red color on the skin or show any opening.
Cysts are another type of blemishes deep down under the skin that can be very painful. They are like pustules in that they are also full of pus. Cysts are mostly likely to cause acne scars, but any acne can create scars if people with acne regularly pick, scratch, or dig at these clogged pores.
For most people acne begins to decrease once they reach their 20's, but some people continue to have acne blemishes into adulthood.
The change in sebum production can also affect the appearance of head hair. Young teens will notice that their hair will become oily or "greasy" more quickly than when they were children. This is because the oil glands at the base of the hair follicles will pump out more oil that coats the base of the hair shaft, making it look oily and weighing it down. Hair may also change in color or texture. Youth with hair that was very blonde or light during childhood may become darker, and more brunette in color. Similarly, youth who had very fine, straight hair may notice their hair becoming more coarse or wavy.