Which hair oils are safe for sensitive scalps?

Which specific carrier + essential oil blends (with exact dilution ratios) safely stimulate hair growth on sensitive, rosacea‑prone scalps?

Answer:
For sensitive, rosacea-prone scalps you must prioritize non-irritating carrier oils that mimic sebum and low-concentration essential oils with proven follicular effects. Recommended base blend and rationale:

• Carrier oils (90–99% of the blend): jojoba oil (liquid wax ester that closely resembles sebum, comedogenic rating ~2), sunflower oil (high in linoleic acid, non‑comedogenic), or fractionated coconut (medium-chain triglycerides; low irritation). These reduce barrier disruption and are less likely to provoke contact dermatitis than high-oleic oils like extra-virgin olive oil.
• Active essential oils (0.5–1% for sensitive scalps): rosemary (evidence from a 2015 randomized trial showed comparable results to 2% minoxidil over 6 months for androgenetic alopecia), and peppermint (promoted hair growth in a 2014 murine study; human evidence still limited). Use a single essential oil at low dilution for safety.
  Practical formula (for a 30 mL bottle):
• 28.5–29.4 mL carrier (95–98%)
• 3 drops rosemary essential oil (≈0.5%) or 6 drops (≈1%) for slightly less-sensitive scalps
  Dilution rules: 0.5% = ~3 drops per 30 mL; 1% = ~6 drops per 30 mL; 2% = ~12 drops per 30 mL. For rosacea-prone or eczema-affected scalps start at 0.25–0.5% and patch test (see later). Keep blends fragrance-free and preservative-free if anhydrous; add preservatives only if you add water or extracts.
  Why this works: jojoba and sunflower protect barrier function and reduce trans-epidermal water loss, while rosemary has human RCT data indicating stimulation of regrowth. Low dilution reduces risk of irritant/allergic reactions on sensitive skin.