(CNN)Amanda Straw estimates that she has read nearly 200 self-help books.
"I'm still looking for the magical one," said the 35-year-old from Hummelstown, Pennsylvania, who has been diagnosed with anxiety, depression, borderline personality disorder and attention-deficit hyperactivity disorder.
Straw gets plenty of professional help. She regularly sees a counselor and takes five medications -- but she can't resist the lure of the self-help section.
"I used to work at my local library, so I'd go through their new books and basically put holds on everything that looks remotely self-help," said Straw, who works at the Hershey Story Museum in Pennsylvania.
She's delved into titles on psychology, neuroscience, productivity and therapy. "The Miracle Morning" by Hal Elrod helped with her morning routine and "Stress Less, Accomplish More" by Emily Fletcher with meditation.
But none of the books has "handed me an easy and effortless cure for all my problems," she said, acknowledging that this is "impossible."
Mental health is a growing crisis around the globe, with roughly 4.4% of the global population affected by depression and 3.6% from anxiety, according to the World Health Organization. While self-help tools, like books or apps, can be beneficial, experts say there can also be pitfalls making these tools ineffective and even harmful.
The self-improvement market -- books, personal coaches, seminars and more -- is a billion-dollar industry in the United States, according to a 2017 report by the independent firm Marketdata. The report values the self-improvement books industry alone at $800 million.
When to reach for that self-help book or app
Timing is crucial for clinical psychologists like Caroline Harris, who is based in the UK.
When people seek help, they are usually in a situation in which the "window of learning" can be harnessed and their motivation is high enough to make changes, she said.
If this window is missed, due to such factors as long doctors' waiting lists, it becomes difficult to effect change, she said. So having cheap and readily available tools like self-help apps or books can be beneficial to some people at the right time.
Harris has worked with a team at the company My Possible Self to create the My Possible Self app, aimed at reducing stress and anxiety, which ensures that "everyone has equal opportunities in mental health support."
Research shows that apps can be effective in managing mental health conditions. A 2013 peer-reviewed trial involved 720 people who experienced mild to moderate depression, anxiety and stress; it showed that a mental health-focused app can bring about "rapid improvements" in symptoms.
The research was carried out by the Black Dog Institute, an Australian research institution for treating and preventing mental illness, which received public and private funding. The institute has a partnership with My Possible Self.
The content tested in the trial has been used to develop a feature in the app that educates users about things like low mood or stress.
"Self-help can be really useful alongside therapy. I think it allows people to maybe normalize mental health problems or reduce stigma. I think it's a massive stepping stone towards people accessing that support," Harris said.
For example, men are known to be less likely to seek professional mental support, according to Harris. People with Asperger's syndrome struggle in social situations and with expressing themselves; they may find apps easier than one-to-one therapy because they're private and easily accessible.
The app's premise is to educate users on where their difficulties are coming from and show them strategies that help with their situation or build resilience. But Harris notes that self-help is not a replacement for therapy.
My Possible Self is one of the apps featured by the UK's National Health Service library. Another, Be Mindful, asks users to complete sessions that include techniques such as video, meditation audio and interactive exercises to reduce stress, depression and anxiety. The app Calm Harm helps people manage urges to self-harm.
'Potentially harmful' advice
Self-help programs can give people the nudge they need to see a psychologist or encourage healthy changes, but that is not always the case, experts say.
Richard E. Redding, a professor of psychology and education at Chapman University, analyzed 50 bestsellers from the self-help bookshelves in 2008.
The most surprising find for Redding was that 18% of the books provided "potentially harmful" advice, such as using herbs to help with problems like depression (there is insufficient or no evidence that this is helpful).
"On the other hand, about 60% of the books provided advice that was grounded in medical and psychological science," Redding added.
Redding's study asked four psychologists with expertise in anxiety and depressive disorders to rate each self-help book on five criteria: how scientifically grounded the book is; whether there are guidelines for self-diagnosis, implementing techniques and monitoring progress; whether the book contains any potentially harmful advice; whether it promotes reasonable expectations about the use and limitations of self-help techniques; and the general usefulness of the book as a self-administered method for changing behavior or psychological change.
"What we found in this study is that the best self-help books targeted very specific problems, like social anxiety or obsessive-compulsive disorder," he said. Very general self-help books, promising to solve all of the reader's problems, "tend to be less valid."
Due to this generalness, the advice is typically not rooted in science, and even if it that is the case, it is not something that a reader can implement in a concrete way, he said.
Happiness isn't a choice
For Svend Brinkmann, author of "Stand Firm: Resisting the Self-Improv