Causes:

Swelling after lip filler injections is a common and expected side effect for many reasons. The primary being that swelling is the body's response to being injected alongside the presence of a foreign substance (the filler). Swelling can be uneven and typically subsides within a few days to a couple of weeks after the procedure as the body adjusts to the filler.

There are other contributing factors to swelling occurring:

1. Trauma: The injection itself causes a certain degree of trauma to the lip tissues. The body responds to this trauma with a localised inflammatory response. Whilst the use of fine needles can help to reduce this side effect,  some level of injury still occurs.

2. Inflammatory Response: This inflammatory response, as discussed, is caused by trauma cause by being injected. The dermal filler is perceived by the body as foreign and therefore activates its immune response. This response includes the release of inflammatory substances, such as histamines and cytokines, which contribute to swelling.

3. Fluid Accumulation: Disrupting the normal balance of fluids in the tissues can lead to an accumulation of fluid in the treated area, causing swelling.

4. Blood Flow Changes: The injection may temporarily affect blood flow in the treated area, contributing to localised swelling.

5. Product-Specific Reactions: Varying formulations in Dermal Fillers may cause different degrees of swelling. For example, hyaluronic acid fillers, which are commonly used for lip augmentation, attracts water molecules, causing temporary swelling.

6. Individual Variation: Everyone's body reacts to each treatment differently.  Some may experience more swelling than others due to their unique physiology and immune response.

One must be aware that excessive or prolonged swelling could be a sign of an adverse reaction or infection. Clients must aftercare instructions provided and to contact their practitioner if they are concerned about swelling or other side effects. 

Aftercare Advice:

Below is conventional aftercare advice for clients post-lip filler injections. It is important to always follow your practitioner's post-treatment instructions and do not hesitate to contact them with any concerns you may have.

1. Cold Compresses: Applying a cold compress or ice packs to the lips can help to reduce inflammation and constrict blood vessels. Ensure you use a clean cloth as barrier between the ice pack and your skin. Do not apply ice directly to the lips.

2. Avoid Alcohol: It's generally recommended to avoid alcohol for the first 24 - 48 hours after the procedure as it can contribute to dehydration, which may exacerbate swelling.

3. Avoiding Blood-Thinning Medications: Some medications, such as aspirin, can increase the risk of bleeding, and thus bruising. 

4. Avoiding physical Activities: Limiting physical activities, especially those that may increase blood flow to the face, can help minimise swelling. Intense exercise and activities that involve bending over or straining should also be avoided.
5. Stay Hydrated: While dehydration can contribute to swelling, maintaining proper hydration is essential for overall well-being and can help support the body's natural healing processes.
6. Arnica Montana: Some clients choose to use topical or an oral form of Arnica Montana as it can help reduce swelling. 
7. Follow-Up with your practitioner: Remember- your practitioner is always there for your safety and comfort. If you are worried about excessive or prolonged swelling, you must contact your practitioner. They can assess the situation and provide guidance on whether any additional interventions or medications may be necessary.

Individuals respond to lip filler injections differently. Always follow the instructions provided by your practitioner and communicate any concerns or questions you may have during the recovery process.