Blue light therapy is a non-invasive treatment that delivers controlled doses of blue-spectrum visible light to the skin or eyes, depending on the condition being treated. At around 415nm, blue light penetrates the upper layers of skin and targets the bacteria responsible for acne. At slightly longer blue and blue-white wavelengths (around 460–470nm), it influences the brain's internal clock through the eyes, making it a useful tool for mood and sleep disorders.

For acne, blue light activates naturally occurring compounds inside Cutibacterium acnes bacteria called porphyrins, which then produce a burst of reactive oxygen that destroys the bacteria from within — no antibiotics needed. For mood and sleep, blue light reaching the retina suppresses melatonin and resets the body's circadian rhythm by signaling 'daytime' to the brain, which can lift mood in people whose internal clocks have drifted — a common problem in winter months or shift workers.

Home devices include LED panels, handheld spot-treatment wands, and wearable silicone masks for acne care, as well as dedicated 10,000-lux light therapy lamps for SAD. Clinical settings use higher-powered LED arrays and sometimes combine blue light with red light or photosensitizing agents (photodynamic therapy/PDT) for more stubborn skin conditions. Quality and wavelength accuracy vary significantly between consumer devices — look for devices that specify their exact wavelength output.

• Acne and breakout-prone skin
• Seasonal affective disorder (SAD)
• Sleep problems and circadian rhythm issues
• Non-seasonal depression
• Skin rejuvenation and fine lines
• Psoriasis (scalp and body)
• Neonatal jaundice
• Shift work sleep disorder
• Jet lag
• Eczema (mild to moderate)

• Recurrence of acne breakouts with ongoing maintenance sessions
• Seasonal mood decline in people with a history of SAD when started proactively in early autumn
• Circadian rhythm drift in shift workers with regular scheduled light exposure

• Tryptophan-rich foods (turkey, eggs, pumpkin seeds) — Tryptophan is the raw material for serotonin — the same neurotransmitter pathway that blue light therapy supports for mood. Eating these foods supports the biological effect of light therapy.
• Tart cherries — One of the few foods with meaningful natural melatonin content, supporting the sleep-regulation goals that blue light therapy is often used alongside.
• Fatty fish (salmon, mackerel, sardines) — Rich in omega-3s and vitamin D, both linked to better mood regulation and reduced seasonal depression — complementary to blue light therapy for SAD.
• Leafy greens (spinach, kale) — Provide magnesium and folate, nutrients involved in serotonin and melatonin synthesis — supporting the mood and sleep pathways that blue light therapy targets.
• Antioxidant-rich foods (blueberries, green tea) — Blue light therapy for skin can mildly increase oxidative stress in tissues; antioxidant-rich foods help counterbalance this and support overall skin health.

• Temporary eye strain or headache (common with SAD lamp sessions — look slightly away from the lamp, not directly at it)
• Mild skin redness or warmth after acne treatment sessions
• Temporary hyperpigmentation (darkening) in darker skin tones — use lower intensities and shorter sessions
• Feeling overstimulated or wired if morning light sessions are too long
• Nausea (occasional, with bright light SAD lamps — usually resolves in the first few days)
• Risk of triggering hypomania or mania in people with bipolar disorder
• Skin dryness after repeated acne treatment sessions
• Eye damage risk if used without proper shielding during skin phototherapy (devices used on the face should shield the eyes)

• Recommended daily: Acne: 15–20 minutes per session, 3–5 sessions per week for 4–8 weeks using a device emitting 40–60 mW/cm² at ~415nm. SAD/mood: 10,000-lux lamp for 20–30 minutes each morning, or lower-lux lamps for longer (e.g. 2,500 lux for 60 minutes). Circadian/sleep: 20–30 minutes of bright blue-enriched light within 30 minutes of waking.
• Best time of day: For mood and sleep: always in the morning, ideally within 30–60 minutes of waking. Evening blue light exposure actively disrupts sleep — avoid. For acne skin treatments: time of day is less critical; morning or midday sessions are generally preferred to avoid any stimulating effects close to bedtime.
• With or without food: Not applicable for skin treatments. For SAD/mood light therapy, many people find it easiest and most effective to use the lamp during breakfast.
• Time to effect: Acne improvement: 4–8 weeks. Mood and SAD: 1–2 weeks of daily use. Sleep and circadian reset: 3–7 days of consistent morning sessions.
• How long to take it: For SAD: use daily throughout autumn and winter; some people continue year-round if they live in low-light climates. For acne: an 8-week initial course, then maintenance 1–2 sessions per week as needed. For sleep/circadian: use daily until the desired shift is established, then as needed for maintenance or during travel.