The S&P 500 share index, which tracks the 500 biggest public companies in the US, hit a milestone by close of business yesterday. It had gone nearly 10 years without a fall of 20% or more.

The index has been lifted by companies such as Apple, Microsoft and Amazon.

Niall Dineen, Senior Fund Manager with Appian Asset Management, explained that a bull run is when an equity market rises without having a 20% correction. The current bull run in equities started after the global financial crisis and it has gone on now for 10 years and markets have risen over 400%.

"I think it has been a great decade for people to be in equity markets but we have to remember a couple of things: number one, this bull market came out of the ashes of the financial crisis so we came from very low levels, and number two, I think this bull market has been driven by a particular type of stock. It has been driven by US growth stocks, and typically when we look back on history and we have a look at other bull markets that have gone on for so long, what we find is that investors almost fall in love with a certain type of stock at particular points in time," Mr Dineen said.

In the 1970s, there was a bull run in US growth stocks, it was called the nifty fifty. There was also the dot com bubble 20 years ago. "I think we're seeing the same type of love-in today," he said. "In previous circumstances, it didn't end well with share price falls of over 70% in both cases so I think there is reason to be cautious."

Is there still room for investors to make money on S&P stocks? "In these particular stocks, I struggle to say yes because I think the risk is there but the reality is I don't know when this love-in with US growth stocks is going to end," Mr Dineen said, "so yes there could possibly be more money to be made, but it is very difficult to make money in any financial asset if you're buying it at all time high valuations."

US stock markets have not been affected by President Donald Trump's political woes. The senior fund manager believes stock markets look past most political events, and the most important driver is economies, "and the most important driver behind this bull market is the low interest rate environment that we have been in."

Mr Dineen believes the big change that will change the markets and that is coming in the next few years, is rising interest rates. 

He said President Trump has the potential to have an effect if he continues with his trade war rhetoric. "If you go to the extreme, the trade war could cause a global recession. With the tariffs he is talking about it would lead to an 8% rise in the price of consumer goods in the US."