What causes dark spots?
Dark spots — also called hyperpigmentation, post-inflammatory hyperpigmentation (PIH), or melasma — occur when melanocytes produce excess melanin in localised areas. Common triggers include sun exposure, inflammation (from acne, eczema, or injury), hormonal changes, and certain medications. Melanin production is controlled by an enzyme called tyrosinase. Most brightening ingredients work by inhibiting tyrosinase or by blocking the transfer of melanin from melanocytes to the skin cells above them.
How kojic acid works
Kojic acid is a naturally derived compound produced during the fermentation of rice, sake, and soy. It inhibits tyrosinase by chelating (binding to) copper ions that the enzyme requires to function. At concentrations of 1–2%, kojic acid reliably reduces the production of melanin. A 2019 study published in the Journal of Drugs in Dermatology found that kojic acid at 1% performed comparably to 4% hydroquinone for melasma over 12 weeks, with fewer irritation events. It is best suited for people with persistent dark spots, uneven skin tone, and post-inflammatory marks.
How tranexamic acid works
Tranexamic acid (TXA) is a synthetic amino acid derivative that works differently from kojic acid. Rather than blocking tyrosinase directly, it inhibits the interaction between keratinocytes and melanocytes — specifically, it blocks plasminogen activator, a compound that stimulates melanocytes to produce melanin in response to UV exposure and inflammation. This makes TXA particularly effective for melasma and PIH. A 2017 randomised controlled trial found that 3% topical tranexamic acid reduced melasma severity scores comparably to 3% hydroquinone over 12 weeks, with a lower incidence of side effects.
Which should you choose?
If your primary concern is uneven skin tone across the whole face: start with kojic acid. It works well for general brightening and is widely tolerated. If your concern is melasma, hormonal hyperpigmentation, or marks that flare after sun exposure: tranexamic acid is often the more targeted choice. Many dermatologists recommend combining both: use a tranexamic acid serum in the morning and a kojic acid treatment at night. Always use SPF 30 or higher during the day — no brightening ingredient is effective without sun protection.
What to avoid when using brightening actives
Avoid combining kojic acid with high-concentration vitamin C or AHA acids in the same application — layering multiple actives at once increases irritation risk. Introduce one new active at a time, patch test first, and give the ingredient 8–12 weeks to show results. Kojic acid can cause photosensitivity, so morning use must be paired with SPF.