An itchy scalp: causes worth checking

The most common and least interesting cause. Shampoo that was not rinsed out properly, conditioner sitting on the scalp, dry shampoo accumulating over several days, or styling product applied too close to the roots.

Test it cheaply: do one careful wash with thorough rinsing, keep conditioner strictly on the mid-lengths and ends, and skip all styling product for a few days. If the itch settles, you have your answer and it costs nothing.

A dry scalp itches. Look for a tight feeling after washing, fine scattered flakes, and dry skin elsewhere on the body. Hot water, frequent washing, harsh cleansers, dry winter air and air conditioning all contribute.

The adjustments are simple: cooler water, gentler shampoo, less frequent washing, and something moisturising on the scalp itself. A light pre-wash oil suits this well.

Persistent itch with larger, greasier, clumping flakes, sometimes with visible pinkness underneath, points here instead. It often extends to the eyebrows or the sides of the nose.

This needs an active ingredient rather than moisture, and it responds to consistency and contact time rather than intensity. Our comparison of dandruff and dry scalp covers the distinction and the actives.

• Hard water leaves mineral deposits on the scalp, which for some people is directly irritating and for others just makes cleansing less effective.
• Chlorinated pool water is drying and irritating with repeated exposure.
• Sweat left to dry, particularly under a helmet or cap, is a common and underrated cause.
• Sun exposure on an exposed parting can leave the scalp sensitised.
• Dust and urban pollution accumulate and add to the load.

Contact irritation or allergy is worth considering if the itch began after introducing something new, or if it is accompanied by redness, small bumps or a rash rather than flaking.

Fragrance and preservatives are common culprits, and botanical ingredients are not exempt: plant extracts and essential oils cause reactions too. Hair dye, particularly permanent dye, is a frequent cause and reactions can develop after years of uneventful use.

If you suspect a product, stop everything new, return to a simple routine, and reintroduce one item at a time. And patch test anything new before applying it fully.

• Tight ponytails, braids and buns, which cause soreness that reads as itch.
• Scratching with nails, which irritates the scalp and creates a self-sustaining cycle.
• Vigorous scrubbing during washing.
• New extensions or a new tight style.

The scratch cycle deserves a mention. Scratching provides seconds of relief and hours of aggravation, and breaking it is often the single most useful thing.

• Intense itch with no visible flaking or obvious cause.
• Thick, well-defined scaly patches, which may be psoriasis.
• Round patches of scaling with hair loss, which can indicate a fungal infection.
• Pustules, crusting, weeping or pain.
• Itch with hair loss in the same area, which needs proper assessment.
• Anything not improving after a few weeks of sensible changes.

Scalp itch is common and usually mundane, but a few causes need diagnosis and prescription treatment. Persisting with shop-bought products for months is the expensive route.