Here's some information I saved, pretty good read.
1) Tissue Irritation
This is probably the most likely cause of post injection pain and the least serious. Tissue irritation is likely to start 12-24 hours after injection, pain can be mild to moderate depending on the level of tissue irritation and the volume injected. The injection site is likely to swell within the muscle, maybe red and likely to be warm and very firm to the touch. The pain and swelling will start to fade after 72 hours and can last over a week in the worst cases. The most likely causes of tissue irritation are:
The hormone crashes out of the solution in the depot. This causes crystallisation of the hormone, this in turn places a lot of pressure on the nerve endings in the muscle belly causing knotting, swelling and pain - this is most common in long chain esters, high mg/ml concentration gear and gear compounded with less than idea oil blends.
A reaction to the acid compounds within the ester. With the metabolic breakdown of the ester attached to the hormone free form acids are released which can cause the muscle tissue rapid irritation at the injection site ***8211; this is most common with propionic acid of the propionate ester. Poor quality raw materials also liberate more freeform acids.
Newb muscles. Of course everyone knows your first injections are the worst. Over time your body will build a tolerance.
Excessive preservative. If too much benzyl alcohol is used to formulate the solution inflammation and pain may result. Pharma grade usually contains 0.9% benzyl alcohol where the common senseu states UGL products contain on average 2%. Anything above 1.2% offers no added anti-microbial effects.
Ice and ibuprofen may help with the swelling. Hot baths, showers and massage of the injection site may help to distribute the injection and reduce pain.
2) Hitting the lymphatic system.
Hitting the lymphatic system is very rare. The lymphatic system is as vast as the circulatory system but the standard injection sights (Glute, ventro-glute, medial delts and vastus lateralis) are generally void of lymphatic nodes. If a lymph node is hit with an injection pain is likely to be severe and edema vast. The swelling will come on very fast and be extensive. It is also likely to travel along the lymph system to the next lymph gland. This is most noticeable with a vastus lateralis shot where the swelling tracks down toward the back of the knee. Unlike the edema experienced with tissue irritation (within the muscle only) the edema with a lymphatic puncture will be both inter and intra-muscular with a moderate amount of swelling just underneath the skin giving it a softer puffy feel. This can be tested for by pressing the swollen area with your finger, if in indent remains you have a more systematic edema and more than just local tissue irreation. The other most noticeable difference is that the swelling should not be warm/hot to touch.
Ice and ibuprofen may help. The affected area must be rested and the patient can expect pain and swelling to start to disperse after 72 hours and last at least 10 days. The painful area must not be massaged.
3) Infection and abscess.
So now to the most serious reason for injection pain. An infection will start in the same manner as tissue irritation with local pain and swelling, with heat and redness around the muscle. The major difference is that after 72 hours tissue irritation should start to subside, if the area is indeed infected this pain and swelling will get worse. The swelling will change in nature becoming more systematic and edema will start to form under the skin becoming softer and more spongy (as described with a lymphatic puncture).
There are many reasons why an infection can manifest, below are some of the most common examples.
Poor injection technique. Correct, and sterile injection technique is a must. You must make sure the injection site and rubber stopper is clean and swabbed with an alcohol wipe.
Also the moisture from the alcohol swab must be allowed to dry before preparing to inject. It is extremely rare but if the alcohol is not allowed to dry the bacterium has not been allowed adequate time to be killed off.
Avoid pinning through a hair follicle or hair and dont be tempted to inject too quickly. Injecting too quickly can increase the risk of infection as this in turn increases injection trauma.
Not rotating injection sites.
The risk of infection is massively increased if the same injection site is used over and over again without giving it time to recover. The more an injury (injection trauma) is irritated (re-injected) the more likely it is to become infected.
Contaminated Gear.
IMO this is probably the least common cause of infection with oil based injections (I cannot say the same for water based injections). This is a no brainer really. Use a reputable UGL or pharma and avoid water based suspensions.
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