Botulinum Toxin Side Effects: What Every Patient Should Know

Botulinum toxin is a widely prescribed aesthetic procedure that helps soften fine lines, reduce wrinkles, and contour facial features.

While well-tolerated by most individuals, it’s important to be informed of potential side effects and how your body may respond after treatment.

This guide explores common and rare effects, including what to expect after treatment around the eyes and forehead.

What Is Botulinum Toxin and How Does It Work?

Botulinum toxin is a purified neurotoxic protein that temporarily blocks the release of acetylcholine, relaxing targeted muscles.

In Singapore, there are several formulations for both medical and cosmetic indications, including wrinkle reduction and treatment of bruxism and excessive sweating.

Other than reducing wrinkles on the face, botulinum injections can help with:

• Excessive sweating (hyperhidrosis)
• Jaw Reduction
• Calf Reduction
• Bladder overactivity

Continue reading to discover more about botulinum toxin’s safety, popular applications, side effects, and more.

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What are the Botulinum Toxin side effects?

Botulinum toxin is permitted in Singapore for both medicinal and aesthetic purposes. The majority of the negative effects are attributable to the fact that it is a neuromodulator that relaxes the muscle by inhibiting nerve impulses.

Most patients will only experience mild side effects, which are temporary with a quick recovery period.

Potential Fever And Chills

Fever and chills are the most commonly reported adverse effects; however, this varies depending on the kind of botulinum toxin administered. The flu-like symptoms disappear after two weeks.

Potential Headache

After botulinum toxin treatment on the forehead for fine wrinkles, a minor headache is common. It only lasts a few hours and will subside after some rest.

Redness/Irritation

Botulinum toxin frequently causes redness at the injection site. Minor skin elevation and redness are its defining features, both of which are treatable with icing. People with sensitive, allergy-prone skin are more likely to experience inflammation.

Pain

The severity of the pain is determined by the region being treated as well as the number of units administered. Although local anaesthetics are used to reduce discomfort, moderate pain is unavoidable because the process includes needles.

Potential Infection

When a needle is inserted, it leaves a tiny wound that can get infected by bacteria found in the skin’s regular flora. However, infection can be avoided by keeping excellent cleanliness before and after treatment. It’s preferable to keep the wound clean until it’s healed.

Swelling

Swelling is an expected side effect of botulinum toxin injections because it is the body’s natural immunological reaction to an injury. It occurs as a result of bleeding from skin blood vessels that the needle has damaged, but it goes away after a few hours.

Eye Discomfort

Because of the eyes’ sensitivity to toxin, the physician must exercise extreme caution while injecting botulinum toxin into the area around the eyes.

Excessive injection can cause temporary dryness of the eyes, brow drooping, impaired vision, and a glaring glare.

All of these adverse effects must be reported to your doctor, even if they subside after 3–4 months.

In very rare cases, some patients may experience botulism-like symptoms. Do seek medical attention right away if you experience the following side effects after a botulinum toxin injection:

• difficulty speaking
• difficulty swallowing
• difficulty breathing
• vision problems
• loss of bladder control
• general weakness

Common Short Term Botulinum Toxin Side Effects

*Always seek professional review if symptoms persist or worsen.

Rare but Serious Risks

Although uncommon, the following events have been documented in clinical literature and post-marketing surveillance. Immediate medical attention is advised if any occur:

• Eyelid or brow ptosis (drooping)

• Difficulty swallowing or speaking

• Generalised muscle weakness

• Allergic reaction (hives, shortness of breath)

Your doctor will discuss personalised risk during consultation.

Who Is at Higher Risk of Side Effects?

1. Individuals with neuromuscular conditions (e.g., myasthenia gravis)

2. Pregnant or breastfeeding patients (treatment generally deferred)

3. Those taking aminoglycoside antibiotics or anticoagulants

4. Patients receiving very high cumulative doses within short intervals

Please provide your complete medical and medication history to ensure that dosing can be appropriately adjusted or avoided as necessary.

What are the Long Term Botulinum Toxin Side Effects?

As the effects of botulinum toxin injections last between 4 and 12 months (depending on the targeted area), most patients who rely on botulinum toxin will require many injections over time.

However, there is insufficient data to accurately determine the effectiveness and negative long-term side effects.

Based on 2015 research, participants are required to have botulinum toxin injections every six months to address bladder issues. It was found that the danger of negative consequences did not grow with time.

People who had many injections showed higher long-term treatment benefits. However, according to the findings of a 2015 study, there are potential harmful effects that may develop after the tenth or eleventh injection.

Is an Allergic Reaction Possible?

Botulinum toxin, like all other medications, can induce allergic reactions in certain patients.

However, an allergic reaction needs prior exposure to the toxin. It might range from moderate itching and redness to a full-blown anaphylactic reaction that can result in death.

To avoid such situations, the patient’s medical history should be shared with the clinic. The patient in the first occurrence of allergy documented recovered without consequences.

How to Reduce the Chance of Side Effects

• Choose a licensed clinic with doctors trained in aesthetic injectables.

• Verify credentials—look for postgraduate certifications in dermatology or aesthetic medicine.

• Follow pre-treatment advice: avoid blood-thinning supplements (vitamin E, fish oil) for one week unless medically indicated.

• Adhere to post-treatment care: stay upright for 4 hours, avoid vigorous exercise, and refrain from massaging treated areas for 24 hours.

• Attend a review visit: 2 weeks later to monitor results and address concerns early.

Botulinum Toxin Side Effects Around the Eyes

The eye area is delicate, and muscle balance is key to natural-looking results. Temporary side effects may include:

• Eyelid drooping (ptosis) – usually caused by diffusion into a nearby muscle

• Uneven eyebrows – can occur if muscle relaxation is imbalanced

• Dry eyes or excessive tearing – due to changes in blinking frequency

These effects are typically short-lived and can improve with time or minor adjustments in subsequent treatments. Skilled injection technique and accurate placement greatly reduce these risks.

Side Effects After Jawline and Masseter Injections

When injected into the masseter muscles for jaw slimming or bruxism relief, botulinum toxin may cause:

• Chewing fatigue, especially when eating tough foods

• Jaw tightness or soreness during the first week

• Asymmetry if muscle strength differs between sides

These reactions usually lessen as the muscles adapt and weaken gradually. Some patients report facial slimming results becoming more noticeable after 4–6 weeks.

Frequently Asked Questions About Botulinum Toxin Side Effects

Can side effects be permanent?
Most adverse effects are temporary. Permanent issues are exceedingly uncommon and usually linked to improper technique or unlicensed products.

Will everyone bruise?
Not always. Bruising risk increases with blood-thinning medications, individual vascularity, and injection depth.

How soon can I repeat treatment?
Most patients repeat every 4–6 months. Shorter intervals may raise antibody-resistance risk.

When to Seek Immediate Help

Call your treating clinic or dial 995 if you experience:

• Breathing difficulty

• Vision changes not resolving within 24 hours

• Severe facial asymmetry within days of treatment

• Signs of infection (increasing redness, warmth, pus)

Medical Disclaimer

This article is intended for general education and does not replace a personal medical consultation. Individual results and risks vary. Consult our doctors to determine if botulinum toxin injections are appropriate for you.