It can be, especially if done improperly.
Popping a Pimple
Some pimples and other acne lesions benefit from being drained or popped in order to remove pus and accelerate healing, but other pimples should be left alone to heal on their own. The nodules and cysts of those patients who suffer from severe inflammatory acne (Acne Type: 4) are often lanced and drained by a dermatologist. This can prevent further damage and limit post-acne scarring.
The important thing is to identify those zits and pimples which can be effectively popped (and which ones can not), and to do that properly and in a sterile fashion. Although it can be tempting to try and pop all zits pimples, in many cases it is more effective to allow the natural progression of the lesion and healing process to take place.
Benefits of Popping a Pimple
Whitehead Pimple Skin and Cellular View
In some cases, it can be beneficial to extract the pus from inside of a pimple. Pus (the white stuff, not the clear fluid) is composed largely of specialized white blood cells called Neutrophils. These white blood cells migrate to the site of infection (the zit) and are designed to destroy and phagocytose (eat) the offending bacteria and other foreign material. These white blood cells are most apparent in open comedome lesions (whitehead pimples).
After accumulating in an acne lesion, the white blood cells release powerful enzymes and free radicals that are designed to kill and digest the source of infection. Unfortunately, these weapons also cause collateral damage to the healthy tissue around the infected follicle. In people who suffer from inflammatory acne, it is often an overeager immune response that causes swelling, redness and discomfort. The collateral damage to healthy tissue during this process is what causes the formation of acne scars.
In acne lesions that are significantly inflamed but easy to drain, removing the pus can limit the amount of collateral damage that occurs and can accelerate the healing process. In addition, the infiltration of the follicle with pus can put a lot of pressure on the surrounding nerves, which can be quite uncomfortable and painful. Draining a lesion may be helpful in relieving this pressure and the accompanying discomfort.
Risks of Popping a Pimple
This Acne Cyst Requires Surgical Extraction
Many acne lesions (especially nodular and cystic acne lesions) can be very difficult to effectively pop and drain. Small, non-inflammatory acne lesions (Acne Types: 1-2) may not contain significant pus that can be drained. In these cases, attempting to drain the lesion can be unhelpful or cause further damage that slows down the healing process and contributes to more acne scarring.
In many acne pimples and cysts it is not just that the follicle is swollen with white blood cells and edema fluid, but rather the entire region of skin tissue is affected. Channels can form in the sub-cutaneous tissue and these channels can be occupied by bacteria laden white blood cells. Non-productive squeezing of pimples in these cases can force these white blood cells (and bacteria) away from the pimple and into the surrounding tissue. This can further spread the underlying infection and inflammation.
Aggressive squeezing of pimples can cause additional damage to the follicle itself, which leads to more inflammation and extends the amount of time it takes for the damage to be repaired. Lancing or popping an acne lesion in a non-sterile fashion can introduce bacteria or foreign material that can lead to more inflammation or even a secondary infection.
In conclusion, there are a lot of things that can go wrong when popping a pimple. Most of these are related to improperly draining a lesion or attempting to drain an unsuitable lesion, or non-sterile technique.