A drug-free, at-home red-light treatment applied to the scalp for pattern hair loss. Evidence best supports a modest but repeatable gain in hair count, with smaller signals for thicker strands and for added benefit alongside a standard scalp treatment. It is very safe but slow, works only on thinning-not-lost follicles, and must be continued to keep gains. (Full Review)

Protocol

Device & Wavelength

650–660 nm red light

Laser comb, wearable cap, or in-clinic helmet

Session

20–30 min, ~3×/week

Some devices specify every-other-day or daily short sessions

Duration

Min. 16–26 weeks

Continued indefinitely to maintain gains

Time to effect

Assessable Response

16–26 weeks

Minimum consistent use before benefit is assessable

Continued Gains

Beyond 26 weeks

Hair-density gains continue to accrue with longer treatment

Maintenance

Indefinite

Gains gradually lost over months after stopping

Benefits

High: Increased hair density in androgenetic alopecia

Medium: Increased hair thickness; additive benefit when combined with topical minoxidil

Low: Slowing or stabilization of ongoing shedding; benefit in chemotherapy-related and other non-androgenetic hair loss

Speculative: Synergy with platelet-rich plasma or microneedling; improved hair-follicle resilience via reduced oxidative stress

Contraindications

Active scalp skin cancer or undiagnosed pigmented scalp lesions (until evaluated)

Photosensitivity disorders (lupus with cutaneous involvement, porphyria)

Scarring alopecia

Key Interactions

Prescription photosensitizers (oral retinoids such as isotretinoin, tetracyclines, fluoroquinolones)

OTC photosensitizers (topical retinoids, some pain relievers)

Photosensitizing supplements (St. John's wort)

Risk & Side Effects

High: Excellent overall tolerability with no serious adverse events

Medium: Transient scalp irritation, dryness, itching, or tingling; temporary increased shedding early in treatment

Low: Eye exposure risk from improper use

Speculative: Theoretical stimulation of pre-existing scalp skin lesions; unknown very-long-term effects of repeated exposure

Monitoring

Marker	Target	Why
Ferritin (iron stores)	≥ 40–70 ng/mL	Low iron stores independently cause shedding and blunt regrowth
TSH (thyroid-stimulating hormone)	~0.5–2.5 mIU/L	Thyroid dysfunction is a common reversible cause of diffuse hair loss
Vitamin D (25-hydroxyvitamin D)	40–60 ng/mL	Deficiency is associated with hair-cycle disruption
Zinc	Mid-to-upper reference range	Zinc deficiency can contribute to hair shedding

Cadence: Baseline labs and photos; standardized photos and density at ~3–4 months, again at 6 months, then every 6–12 months. Blood markers rechecked only if a deficiency was found or symptoms suggest one.

Qualitative Assessment

Reduced daily shedding (fewer hairs in the shower drain or on the pillow)
Perceived increase in density, coverage, or scalp "show-through" in consistent lighting
Improved hair-shaft thickness and manageability
Regrowth of finer "baby" hairs along thinning areas
Overall confidence and satisfaction with appearance

Low-Level Light Therapy for Hair Regrowth

Protocol

Benefits

Risk & Side Effects

Monitoring

Qualitative Assessment