Quick replies, longer reasons

Not automatically. Safety depends on the specific ingredient, its concentration and your skin. Plenty of natural substances are allergens, and plenty of lab-made ones are very gentle. Full thread.

Apply a small amount to the inner forearm or behind the ear, then wait 48 hours. For leave-on products, some dermatologists suggest repeating twice daily for a week. Redness, itching or swelling means stop.

Some dry-skinned people tolerate it well, but it often clogs pores on acne-prone faces. It shines on body skin, cuticles and hair ends. See the oil table.

Many contain recognised fragrance allergens such as linalool and limonene, and some citrus oils are phototoxic. Never apply them neat; if your skin is sensitive, skip them.

No. SPF cannot be measured at home, and stirring zinc oxide into oil gives uneven, unknown protection. Use a tested product. DIY safety list.

It has no legal or scientific definition. Each retailer or brand writes its own list of excluded ingredients, and those lists often disagree.

Often, yes, particularly preservative-free creams and linoleic-rich oils like rosehip. Check the open-jar symbol (for example "6M") and keep products away from heat and sunlight.

They stop bacteria and mould growing in water-based products. A few, such as methylisothiazolinone, have caused allergy outbreaks and are now restricted in the EU, but an unpreserved cream can become contaminated within days.

No. COSMOS and similar schemes certify how ingredients are farmed and processed. Certified products can still contain fragrance and essential oils. Gentle swaps.