Melanogenesis
Melanogenesis — the biological process by which melanocytes produce melanin, driven by the enzyme tyrosinase and triggered by factors such as UV exposure. It takes place inside specialized structures called melanosomes, which are then transferred to surrounding skin cells to influence pigmentation.
Key points
- Melanogenesis is the multi-step synthesis of melanin inside melanocytes.
- The enzyme tyrosinase is a key rate-limiting driver of the process.
- UV radiation is a major trigger that stimulates increased melanin production and tanning.
- Melanin is produced within organelles called melanosomes and then passed to keratinocytes.
- Many brightening ingredients aim to influence steps in melanogenesis, such as inhibiting tyrosinase.
The pathway, step by step
| Step | What happens | What can influence it |
|---|---|---|
| 1. Signal arrives | UV, hormones or inflammatory mediators reach the melanocyte | UVB dose, visible light, oestrogen, wound or spot healing |
| 2. Receptor response | Alpha-MSH binds MC1R, raising cyclic AMP and the MITF transcription factor | MC1R gene variants blunt the signal in some people |
| 3. Enzymes made | MITF switches on tyrosinase and the tyrosinase-related proteins | Copper supply, melanosome pH, genetic background |
| 4. Tyrosine to dopaquinone | Tyrosinase converts tyrosine to DOPA, then DOPA to dopaquinone — the rate-limiting stretch | Tyrosinase activity, the target of most tyrosinase-inhibiting ingredients |
| 5. Branch point | Dopaquinone becomes eumelanin, or joins cysteine and becomes pheomelanin | Cysteine availability inside the melanosome |
| 6. Melanosome matures | Pigment is laid on a protein scaffold through four stages | Scaffold proteins, transport along the melanocyte dendrites |
| 7. Transfer | Mature melanosomes pass into surrounding keratinocytes and cap their nuclei | Keratinocyte receptor activity, rate of cell turnover |
From tyrosine to pigment
Synthesis begins with the amino acid tyrosine. Tyrosinase, a copper-dependent enzyme, hydroxylates tyrosine to DOPA and then oxidises DOPA to dopaquinone. That stretch is rate-limiting: most of what follows proceeds with little further enzymatic push, so tyrosinase activity is the pathway's main control point.
Dopaquinone is where the two pigments part company. With cysteine present it forms cysteinyldopa and runs towards yellow-red pheomelanin; without it, it cyclises and, helped by tyrosinase-related proteins, builds brown-black eumelanin. The pigment is laid on a protein scaffold inside the melanosome, which matures through four stages from an unpigmented vesicle to a fully pigmented granule.
What turns the pathway up
UVB damages keratinocyte DNA, and the repair response raises p53, which drives production of pro-opiomelanocortin and the release of alpha-melanocyte-stimulating hormone. Alpha-MSH binds MC1R on the melanocyte, lifting cyclic AMP and MITF, and tyrosinase output rises. Common MC1R variants weaken this loop, which is part of why some people freckle rather than tan.
Other inputs feed in as well. Oestrogen and progesterone influence melanocyte activity, which is one reason pigmentation can shift during pregnancy; visible light and UVA contribute independently of UVB; and melanosome pH and copper supply set how efficiently the enzymes work. Finished melanosomes must still reach keratinocytes, so transfer and turnover shape what is visible.
Why inflammation leaves a mark
Inflammation is itself a pigment signal. Mediators released during spots, eczema, friction or a burn — prostaglandins, leukotrienes and various cytokines — stimulate nearby melanocytes directly, so skin can heal with a darker patch where the inflammation was. This is post-inflammatory hyperpigmentation.
Where inflammation disturbs the basal layer, pigment can drop into the dermis and be taken up by macrophages, and pigment held there clears far more slowly than pigment in the epidermis. Melasma, vitiligo and other pigmentary conditions involve different mechanisms again; diagnosis and treatment belong with a clinician rather than with self-assessment.
Frequently asked
How do skin-brightening ingredients relate to melanogenesis?
Many brightening ingredients work by interfering with steps in melanogenesis, often by inhibiting the enzyme tyrosinase or slowing melanin transfer. This can help reduce the appearance of excess pigmentation over time.
Why does skin tan after sun exposure?
UV exposure stimulates melanogenesis, prompting melanocytes to produce more melanin as a protective response, which appears as tanning. This increased pigment offers limited UV protection but also reflects underlying skin stress.
How long does new pigment take to show up?
Existing melanin darkens within minutes through simple oxidation, which is why skin can look different the same afternoon. Newly synthesised pigment is slower, generally becoming visible over a few days and peaking around a week after exposure.
Is melanogenesis the same thing as pigmentation?
No. Melanogenesis is the manufacturing process inside the melanocyte; pigmentation is the visible result once melanosomes have been handed to keratinocytes and carried towards the surface. Pigmentation can therefore change through transfer and turnover, not only synthesis.
Does visible light trigger it as well as UV?
Yes. High-energy visible light and UVA can both stimulate pigment production, and in more pigmented skin the response to visible light tends to be more persistent than the response to UVB alone.
Does the same process colour hair?
Broadly, yes: follicular melanocytes make melanin and pass it to the growing hair shaft. Hair pigmentation runs in cycles rather than continuously, and greying reflects a decline in those follicular melanocytes rather than anything in the epidermis.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
