I've heard that if you pull out a grey hair, two will grow in its place. Is this true? If I start pulling out my first few grey hairs, will it just encourage more?
If you pull out a hair by its root, another will eventually grow back from the same follicle (the structure in the skin from which hairs grow), but not two. Just one. A hair becomes grey because its follicle loses the ability to fill its interior with pigment. Instead, the centre of the hair is filled with air. Reflection of light from that air makes the hair appear silvery. As you grow older, more and more hair follicles will switch from pigment-producers to air-producers, hence the gradual switch to grey. Pulling out the white hairs won't slow or hasten that process: it will just happen at its own pace. What you do about it is a cosmetic, not a medical, problem.

Do allergic reactions last for life? Last time I tried to chop a fresh chilli, I had an alarming reaction: my chest tightened as if I had a band around it and I couldn't breathe. I rushed into the garden, and in the fresh air the symptoms disappeared in seconds. Would it be safe for me to chop fresh chilli again?
I'm not sure you had an allergic reaction, and it is odd that the fresh air cleared it so quickly. The chilli may have irritated your throat, but that wasn't necessarily an allergic response. Talk to your doctor about this in more detail, and don't attempt to chop fresh chilli until he or she gives you the all-clear. As for allergies being lifelong, that isn't always the case. For example, many people with hay fever find that it peaks in their teens and 20s and dies off by their 40s. In older age, the allergic immune response can become much weaker. There are always exceptions, however. Asthma, for example, can start around the menopause in a few women. Everyone has a unique allergy history, which is why you should see your doctor before exposing yourself to the possibility, however unlikely, of a severe reaction.

• Got a medical query for Dr Tom? Email doctordoctor@theguardian.com