What's happening?

The stock market is booming. The start of 2018 trading has seen new records set on the Nasdaq and the S&P 500, with the Dow Jones Industrial Average also surging, Fortune reports.

CNBC reports this is following on from a strong 2017 for major companies, with growth in corporate earnings and positive economic data sending company values skyrocketing.

And stocks got a further boost at the end of 2017 when the GOP passed a tax bill that included huge business tax cuts.

But it's not good for everyone?

Surging shares is obviously good news for public companies listed on stock markets, as well as the major shareholders in said companies (ie. the rich).

And there are plenty of regular Americans who have money invested in the stock market, whether by holding stocks and funds in regular trading accounts, or through their IRA and 401(k) retirement accounts.

But while the stock market is being lauded as a sign of economic strength, it doesn't have direct benefits for almost half of Americans.

A Gallup survey last year found that just 54 percent of Americans own stocks, a drop from 62 percent since the financial crisis.

This means that 46 percent of U.S. adults have no skin in the game, so to speak, and most of these are among the youngest and poorest Americans.

Unsurprisingly it's the richest in society who benefit the most from a booming stock market.

As of 2013, NPR reports that the top 10 percent of American earners owned on average $969,000 in stocks, with the next 40 percent owning $132,000 on average and the bottom 50 percent just under $54,000. 

So these people lose out?

It's not to say there's no indirect benefit to the middle and lower classes without money invested in the stock market.

A booming market means more money for the wealthy, who spend more and help smaller businesses and local economies as a result. Companies meanwhile may increase investment in their business, creating jobs and potentially growing wages.

But there remains a continued debate as to how much it truly does "trickle down" to lower income workers. At the very least, a booming stock market doesn't see companies take action as quickly as, say a stock market crash, which has historically prompted them to quickly slash jobs and freeze wages. 

Despite the stock market growth seen over the past few years, Glassdoor reported last month that year-on-year wage growth in the U.S. was just 1.1 percent.

As NPR notes, with the top 20 percent earners owning 92 percent of stocks, highlighting the stock market as a measure of economic success "isn't very relevant to many Americans."