I've always had dandruff, but lately it's been getting worse and what used to help no longer is. what could cause it to get worse so quickly?

Seborrheic dermatiti: is a common skin condition that causes scaly patches, red skin and stubborn dandruff. Flare ups can occur for not apparent reason, resulting in worsening of dandruff. Seborrheic dermatitis doesn't affect your overall health, but can be uncomfortable and cause embarrassment. It isn't contagious, and it's not a sign of poor personal hygiene. Nizoral (ketoconazole) shampoo is usually very helpful.