What does botulinum toxin injection treat? Effects on expression lines and duration guidance

Botulinum toxin injection temporarily weakens the muscles that create facial expressions, making wrinkles that form from movement—such as between the eyebrows or at the corners of the eyes—less noticeable[1]. Muscle movement typically stops within 5–15 days after injection, and the effect is described as lasting approximately 4–6 months[1]. The effect does not last indefinitely, and side effects such as drooping eyelids can occur.

What types of wrinkles does it treat?

It is most effective for expression lines that form when smiling or frowning. The wrinkles most extensively studied in research are those between the eyebrows, at the corners of the eyes, and on the forehead[1].

For wrinkles between the eyebrows, reduction at the 4-week mark after injection has been confirmed in many comparative trials[1]. Treatment for expression lines is strongly recommended in guidelines from the Japan Association of Plastic Surgeons[2].

When does it start working and how long does it last?

It typically starts working several days after injection, and duration is usually measured in months. Textbooks describe the effect as appearing within 3–10 days and lasting 3–6 months as the general standard[3].

Results vary between individuals. Factors such as skin quality, age, sex, and the baseline depth of wrinkles are thought to affect outcomes[4]. Even at the same dose, duration can vary.

What does it not work well for?

The effect is temporary, and repeated injections are necessary if you wish to maintain results[1][3]. However, the long-term effects and side effects of repeated treatments have not yet been sufficiently studied[1].

Difficulty also varies by location. The lower eyelid has thin skin, and complications such as sagging (skin laxity), puffiness under the eye, and double vision are more likely to occur, making it considered an advanced technique[5].

What side effects should I be aware of?

The most important to know is drooping eyelids. Research summaries report that injection probably increases the risk of eyelid drooping[1].

Eyebrow shape may not turn out as expected. Because facial structure varies among individuals, a standardized injection technique makes eyebrow shape difficult to predict, and drooping of the eyebrows or eyelids can occur[6]. It is important to have the injection site customized to your own facial structure[6].

Do different formulations have different effects?

Yes. Dosing methods differ by formulation, and the "units" of one formulation cannot be directly converted to units of another[7].

It has been noted that direct head-to-head research comparing major formulations is still insufficient[1]. Do not hesitate to ask which formulation and how many units will be used.

What should a consultation confirm to see if it is right for you?

First, whether the wrinkles that concern you are expression lines that move with facial movement. Next, share the position of your eyebrows and eyelids and any prior injection experience[6].

Where, which formulation, and how much to inject cannot be decided from an article alone. During consultation, have your face examined while moving your expression, and confirm the expected onset time and duration.